diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7cd70e709..b88da3c3d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,30 @@
+Changes in [9.8.0](https://github.com/matrix-org/matrix-js-sdk/releases/tag/v9.8.0) (2021-03-01)
+================================================================================================
+[Full Changelog](https://github.com/matrix-org/matrix-js-sdk/compare/v9.8.0-rc.1...v9.8.0)
+
+ * No changes since rc.1
+
+Changes in [9.8.0-rc.1](https://github.com/matrix-org/matrix-js-sdk/releases/tag/v9.8.0-rc.1) (2021-02-24)
+==========================================================================================================
+[Full Changelog](https://github.com/matrix-org/matrix-js-sdk/compare/v9.7.0...v9.8.0-rc.1)
+
+ * Optimise prefixed logger
+   [\#1615](https://github.com/matrix-org/matrix-js-sdk/pull/1615)
+ * Add debug logs to encryption prep, take 3
+   [\#1614](https://github.com/matrix-org/matrix-js-sdk/pull/1614)
+ * Add functions for upper & lowercase random strings
+   [\#1612](https://github.com/matrix-org/matrix-js-sdk/pull/1612)
+ * Room helpers for invite permissions and join rules
+   [\#1609](https://github.com/matrix-org/matrix-js-sdk/pull/1609)
+ * Fixed wording in "Adding video track with id" log
+   [\#1606](https://github.com/matrix-org/matrix-js-sdk/pull/1606)
+ * Add more debug logs to encryption prep
+   [\#1605](https://github.com/matrix-org/matrix-js-sdk/pull/1605)
+ * Add option to set ice candidate pool size
+   [\#1604](https://github.com/matrix-org/matrix-js-sdk/pull/1604)
+ * Cancel call if no source was selected
+   [\#1601](https://github.com/matrix-org/matrix-js-sdk/pull/1601)
+
 Changes in [9.7.0](https://github.com/matrix-org/matrix-js-sdk/releases/tag/v9.7.0) (2021-02-16)
 ================================================================================================
 [Full Changelog](https://github.com/matrix-org/matrix-js-sdk/compare/v9.7.0-rc.1...v9.7.0)
diff --git a/package.json b/package.json
index a963428b7..f9fafb132 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "matrix-js-sdk",
-  "version": "9.7.0",
+  "version": "9.8.0",
   "description": "Matrix Client-Server SDK for Javascript",
   "scripts": {
     "prepublishOnly": "yarn build",
@@ -15,7 +15,7 @@
     "build:minify-browser": "terser dist/browser-matrix.js --compress --mangle --source-map --output dist/browser-matrix.min.js",
     "gendoc": "jsdoc -c jsdoc.json -P package.json",
     "lint": "yarn lint:types && yarn lint:js",
-    "lint:js": "eslint --max-warnings 73 src spec",
+    "lint:js": "eslint --max-warnings 72 src spec",
     "lint:types": "tsc --noEmit",
     "test": "jest spec/ --coverage --testEnvironment node",
     "test:watch": "jest spec/ --coverage --testEnvironment node --watch"
diff --git a/spec/unit/crypto/algorithms/olm.spec.js b/spec/unit/crypto/algorithms/olm.spec.js
index 0efe74e77..c548355b5 100644
--- a/spec/unit/crypto/algorithms/olm.spec.js
+++ b/spec/unit/crypto/algorithms/olm.spec.js
@@ -190,5 +190,91 @@ describe("OlmDevice", function() {
             // new session and will have called claimOneTimeKeys
             expect(count).toBe(2);
         });
+
+        it("avoids deadlocks when two tasks are ensuring the same devices", async function() {
+            // This test checks whether `ensureOlmSessionsForDevices` properly
+            // handles multiple tasks in flight ensuring some set of devices in
+            // common without deadlocks.
+
+            let claimRequestCount = 0;
+            const baseApis = {
+                claimOneTimeKeys: () => {
+                    // simulate a very slow server (.5 seconds to respond)
+                    claimRequestCount++;
+                    return new Promise((resolve, reject) => {
+                        setTimeout(reject, 500);
+                    });
+                },
+            };
+
+            const deviceBobA = DeviceInfo.fromStorage({
+                keys: {
+                    "curve25519:BOB-A": "akey",
+                },
+            }, "BOB-A");
+            const deviceBobB = DeviceInfo.fromStorage({
+                keys: {
+                    "curve25519:BOB-B": "bkey",
+                },
+            }, "BOB-B");
+
+            // There's no required ordering of devices per user, so here we
+            // create two different orderings so that each task reserves a
+            // device the other task needs before continuing.
+            const devicesByUserAB = {
+                "@bob:example.com": [
+                    deviceBobA,
+                    deviceBobB,
+                ],
+            };
+            const devicesByUserBA = {
+                "@bob:example.com": [
+                    deviceBobB,
+                    deviceBobA,
+                ],
+            };
+
+            function alwaysSucceed(promise) {
+                // swallow any exception thrown by a promise, so that
+                // Promise.all doesn't abort
+                return promise.catch(() => {});
+            }
+
+            const task1 = alwaysSucceed(olmlib.ensureOlmSessionsForDevices(
+                aliceOlmDevice, baseApis, devicesByUserAB,
+            ));
+
+            // After a single tick through the first task, it should have
+            // claimed ownership of all devices to avoid deadlocking others.
+            expect(Object.keys(aliceOlmDevice._sessionsInProgress).length).toBe(2);
+
+            const task2 = alwaysSucceed(olmlib.ensureOlmSessionsForDevices(
+                aliceOlmDevice, baseApis, devicesByUserBA,
+            ));
+
+            // The second task should not have changed the ownership count, as
+            // it's waiting on the first task.
+            expect(Object.keys(aliceOlmDevice._sessionsInProgress).length).toBe(2);
+
+            // Track the tasks, but don't await them yet.
+            const promises = Promise.all([
+                task1,
+                task2,
+            ]);
+
+            await new Promise((resolve) => {
+                setTimeout(resolve, 200);
+            });
+
+            // After .2s, the first task should have made an initial claim request.
+            expect(claimRequestCount).toBe(1);
+
+            await promises;
+
+            // After waiting for both tasks to complete, the first task should
+            // have failed, so the second task should have tried to create a
+            // new session and will have called claimOneTimeKeys
+            expect(claimRequestCount).toBe(2);
+        });
     });
 });
diff --git a/spec/unit/webrtc/call.spec.ts b/spec/unit/webrtc/call.spec.ts
index 06da02502..7336a7371 100644
--- a/spec/unit/webrtc/call.spec.ts
+++ b/spec/unit/webrtc/call.spec.ts
@@ -190,4 +190,62 @@ describe('Call', function() {
         // Hangup to stop timers
         call.hangup(CallErrorCode.UserHangup, true);
     });
+
+    it('should add candidates received before answer if party ID is correct', async function() {
+        await call.placeVoiceCall();
+        call.peerConn.addIceCandidate = jest.fn();
+
+        call.onRemoteIceCandidatesReceived({
+            getContent: () => {
+                return {
+                    version: 1,
+                    call_id: call.callId,
+                    party_id: 'the_correct_party_id',
+                    candidates: [
+                        {
+                            candidate: 'the_correct_candidate',
+                            sdpMid: '',
+                        },
+                    ],
+                };
+            },
+        });
+
+        call.onRemoteIceCandidatesReceived({
+            getContent: () => {
+                return {
+                    version: 1,
+                    call_id: call.callId,
+                    party_id: 'some_other_party_id',
+                    candidates: [
+                        {
+                            candidate: 'the_wrong_candidate',
+                            sdpMid: '',
+                        },
+                    ],
+                };
+            },
+        });
+
+        expect(call.peerConn.addIceCandidate.mock.calls.length).toBe(0);
+
+        await call.onAnswerReceived({
+            getContent: () => {
+                return {
+                    version: 1,
+                    call_id: call.callId,
+                    party_id: 'the_correct_party_id',
+                    answer: {
+                        sdp: DUMMY_SDP,
+                    },
+                };
+            },
+        });
+
+        expect(call.peerConn.addIceCandidate.mock.calls.length).toBe(1);
+        expect(call.peerConn.addIceCandidate).toHaveBeenCalledWith({
+            candidate: 'the_correct_candidate',
+            sdpMid: '',
+        });
+    });
 });
diff --git a/src/@types/event.ts b/src/@types/event.ts
index d54920a62..adffcd560 100644
--- a/src/@types/event.ts
+++ b/src/@types/event.ts
@@ -36,6 +36,10 @@ export enum EventType {
      */
     RoomAliases = "m.room.aliases", // deprecated https://matrix.org/docs/spec/client_server/r0.6.1#historical-events
 
+    // Spaces MSC1772
+    SpaceChild = "org.matrix.msc1772.space.child",
+    SpaceParent = "org.matrix.msc1772.space.parent",
+
     // Room timeline events
     RoomRedaction = "m.room.redaction",
     RoomMessage = "m.room.message",
@@ -87,3 +91,9 @@ export enum MsgType {
     Location = "m.location",
     Video = "m.video",
 }
+
+export const RoomCreateTypeField = "org.matrix.msc1772.type"; // Spaces MSC1772
+
+export enum RoomType {
+    Space = "org.matrix.msc1772.space", // Spaces MSC1772
+}
diff --git a/src/base-apis.js b/src/base-apis.js
index 07694596b..37c3d76d6 100644
--- a/src/base-apis.js
+++ b/src/base-apis.js
@@ -2374,3 +2374,26 @@ MatrixBaseApis.prototype.reportEvent = function(roomId, eventId, score, reason)
     return this._http.authedRequest(undefined, "POST", path, null, {score, reason});
 };
 
+/**
+ * Fetches or paginates a summary of a space as defined by MSC2946
+ * @param {string} roomId The ID of the space-room to use as the root of the summary.
+ * @param {number?} maxRoomsPerSpace The maximum number of rooms to return per subspace.
+ * @param {boolean?} autoJoinOnly Whether to only return rooms with auto_join=true.
+ * @param {number?} limit The maximum number of rooms to return in total.
+ * @param {string?} batch The opaque token to paginate a previous summary request.
+ * @returns {Promise} the response, with next_batch, rooms, events fields.
+ */
+MatrixBaseApis.prototype.getSpaceSummary = function(roomId, maxRoomsPerSpace, autoJoinOnly, limit, batch) {
+    const path = utils.encodeUri("/rooms/$roomId/spaces", {
+        $roomId: roomId,
+    });
+
+    return this._http.authedRequest(undefined, "POST", path, null, {
+        max_rooms_per_space: maxRoomsPerSpace,
+        auto_join_only: autoJoinOnly,
+        limit,
+        batch,
+    }, {
+        prefix: "/_matrix/client/unstable/org.matrix.msc2946",
+    });
+};
diff --git a/src/client.js b/src/client.js
index 5e224a5bf..4be20f8c0 100644
--- a/src/client.js
+++ b/src/client.js
@@ -393,6 +393,9 @@ export function MatrixClient(opts) {
     this._clientWellKnown = undefined;
     this._clientWellKnownPromise = undefined;
 
+    this._turnServers = [];
+    this._turnServersExpiry = null;
+
     // The SDK doesn't really provide a clean way for events to recalculate the push
     // actions for themselves, so we have to kinda help them out when they are encrypted.
     // We do this so that push rules are correctly executed on events in their decrypted
@@ -4942,6 +4945,15 @@ MatrixClient.prototype.getTurnServers = function() {
     return this._turnServers || [];
 };
 
+/**
+ * Get the unix timestamp (in seconds) at which the current
+ * TURN credentials (from getTurnServers) expire
+ * @return {number} The expiry timestamp, in seconds, or null if no credentials
+ */
+MatrixClient.prototype.getTurnServersExpiry = function() {
+    return this._turnServersExpiry;
+};
+
 /**
  * Set whether to allow a fallback ICE server should be used for negotiating a
  * WebRTC connection if the homeserver doesn't provide any servers. Defaults to
@@ -5413,6 +5425,9 @@ async function(roomId, eventId, relationType, eventType, opts = {}) {
         }));
         events = events.filter(e => e.getType() === eventType);
     }
+    if (originalEvent && relationType === "m.replace") {
+        events = events.filter(e => e.getSender() === originalEvent.getSender());
+    }
     return {
         originalEvent,
         events,
@@ -5437,6 +5452,7 @@ function checkTurnServers(client) {
                 credential: res.password,
             };
             client._turnServers = [servers];
+            client._turnServersExpiry = Date.now() + res.ttl;
             // re-fetch when we're about to reach the TTL
             client._checkTurnServersTimeoutID = setTimeout(() => {
                 checkTurnServers(client);
diff --git a/src/crypto/OlmDevice.js b/src/crypto/OlmDevice.js
index 24565507d..0989d19f3 100644
--- a/src/crypto/OlmDevice.js
+++ b/src/crypto/OlmDevice.js
@@ -545,6 +545,7 @@ OlmDevice.prototype.createOutboundSession = async function(
                 }
             });
         },
+        logger.withPrefix("[createOutboundSession]"),
     );
     return newSessionId;
 };
@@ -605,6 +606,7 @@ OlmDevice.prototype.createInboundSession = async function(
                 }
             });
         },
+        logger.withPrefix("[createInboundSession]"),
     );
 
     return result;
@@ -619,8 +621,10 @@ OlmDevice.prototype.createInboundSession = async function(
  * @return {Promise<string[]>}  a list of known session ids for the device
  */
 OlmDevice.prototype.getSessionIdsForDevice = async function(theirDeviceIdentityKey) {
+    const log = logger.withPrefix("[getSessionIdsForDevice]");
+
     if (this._sessionsInProgress[theirDeviceIdentityKey]) {
-        logger.log("waiting for olm session to be created");
+        log.debug(`Waiting for Olm session for ${theirDeviceIdentityKey} to be created`);
         try {
             await this._sessionsInProgress[theirDeviceIdentityKey];
         } catch (e) {
@@ -638,6 +642,7 @@ OlmDevice.prototype.getSessionIdsForDevice = async function(theirDeviceIdentityK
                 },
             );
         },
+        log,
     );
 
     return sessionIds;
@@ -651,13 +656,14 @@ OlmDevice.prototype.getSessionIdsForDevice = async function(theirDeviceIdentityK
  * @param {boolean} nowait Don't wait for an in-progress session to complete.
  *     This should only be set to true of the calling function is the function
  *     that marked the session as being in-progress.
+ * @param {Logger} [log] A possibly customised log
  * @return {Promise<?string>}  session id, or null if no established session
  */
 OlmDevice.prototype.getSessionIdForDevice = async function(
-    theirDeviceIdentityKey, nowait,
+    theirDeviceIdentityKey, nowait, log,
 ) {
     const sessionInfos = await this.getSessionInfoForDevice(
-        theirDeviceIdentityKey, nowait,
+        theirDeviceIdentityKey, nowait, log,
     );
 
     if (sessionInfos.length === 0) {
@@ -697,11 +703,16 @@ OlmDevice.prototype.getSessionIdForDevice = async function(
  * @param {boolean} nowait Don't wait for an in-progress session to complete.
  *     This should only be set to true of the calling function is the function
  *     that marked the session as being in-progress.
+ * @param {Logger} [log] A possibly customised log
  * @return {Array.<{sessionId: string, hasReceivedMessage: Boolean}>}
  */
-OlmDevice.prototype.getSessionInfoForDevice = async function(deviceIdentityKey, nowait) {
+OlmDevice.prototype.getSessionInfoForDevice = async function(
+    deviceIdentityKey, nowait, log = logger,
+) {
+    log = log.withPrefix("[getSessionInfoForDevice]");
+
     if (this._sessionsInProgress[deviceIdentityKey] && !nowait) {
-        logger.log("waiting for olm session to be created");
+        log.debug(`Waiting for Olm session for ${deviceIdentityKey} to be created`);
         try {
             await this._sessionsInProgress[deviceIdentityKey];
         } catch (e) {
@@ -727,6 +738,7 @@ OlmDevice.prototype.getSessionInfoForDevice = async function(deviceIdentityKey,
                 }
             });
         },
+        log,
     );
 
     return info;
@@ -761,6 +773,7 @@ OlmDevice.prototype.encryptMessage = async function(
                 this._saveSession(theirDeviceIdentityKey, sessionInfo, txn);
             });
         },
+        logger.withPrefix("[encryptMessage]"),
     );
     return res;
 };
@@ -794,6 +807,7 @@ OlmDevice.prototype.decryptMessage = async function(
                 this._saveSession(theirDeviceIdentityKey, sessionInfo, txn);
             });
         },
+        logger.withPrefix("[decryptMessage]"),
     );
     return payloadString;
 };
@@ -825,6 +839,7 @@ OlmDevice.prototype.matchesSession = async function(
                 matches = sessionInfo.session.matches_inbound(ciphertext);
             });
         },
+        logger.withPrefix("[matchesSession]"),
     );
     return matches;
 };
@@ -1095,6 +1110,7 @@ OlmDevice.prototype.addInboundGroupSession = async function(
                 },
             );
         },
+        logger.withPrefix("[addInboundGroupSession]"),
     );
 };
 
@@ -1265,6 +1281,7 @@ OlmDevice.prototype.decryptGroupMessage = async function(
                 },
             );
         },
+        logger.withPrefix("[decryptGroupMessage]"),
     );
 
     if (error) {
@@ -1310,6 +1327,7 @@ OlmDevice.prototype.hasInboundSessionKeys = async function(roomId, senderKey, se
                 },
             );
         },
+        logger.withPrefix("[hasInboundSessionKeys]"),
     );
 
     return result;
@@ -1369,6 +1387,7 @@ OlmDevice.prototype.getInboundGroupSessionKey = async function(
                 },
             );
         },
+        logger.withPrefix("[getInboundGroupSessionKey]"),
     );
 
     return result;
diff --git a/src/crypto/algorithms/megolm.js b/src/crypto/algorithms/megolm.js
index 0fa3d046d..7ea048d2b 100644
--- a/src/crypto/algorithms/megolm.js
+++ b/src/crypto/algorithms/megolm.js
@@ -271,7 +271,7 @@ MegolmEncryption.prototype._ensureOutboundSession = async function(
                 logger.debug(`Shared keys with existing Olm sessions in ${this._roomId}`);
             })(),
             (async () => {
-                logger.debug(`Sharing keys with new Olm sessions in ${this._roomId}`);
+                logger.debug(`Sharing keys (start phase 1) with new Olm sessions in ${this._roomId}`);
                 const errorDevices = [];
 
                 // meanwhile, establish olm sessions for devices that we don't
@@ -285,6 +285,7 @@ MegolmEncryption.prototype._ensureOutboundSession = async function(
                     session, key, payload, devicesWithoutSession, errorDevices,
                     singleOlmCreationPhase ? 10000 : 2000, failedServers,
                 );
+                logger.debug(`Shared keys (end phase 1) with new Olm sessions in ${this._roomId}`);
 
                 if (!singleOlmCreationPhase && (Date.now() - start < 10000)) {
                     // perform the second phase of olm session creation if requested,
@@ -313,21 +314,24 @@ MegolmEncryption.prototype._ensureOutboundSession = async function(
                             }
                         }
 
+                        logger.debug(`Sharing keys (start phase 2) with new Olm sessions in ${this._roomId}`);
                         await this._shareKeyWithDevices(
                             session, key, payload, retryDevices, failedDevices, 30000,
                         );
+                        logger.debug(`Shared keys (end phase 2) with new Olm sessions in ${this._roomId}`);
 
                         await this._notifyFailedOlmDevices(session, key, failedDevices);
                     })();
                 } else {
                     await this._notifyFailedOlmDevices(session, key, errorDevices);
                 }
-                logger.debug(`Shared keys with new Olm sessions in ${this._roomId}`);
+                logger.debug(`Shared keys (all phases done) with new Olm sessions in ${this._roomId}`);
             })(),
             (async () => {
                 logger.debug(`Notifying blocked devices in ${this._roomId}`);
                 // also, notify blocked devices that they're blocked
                 const blockedMap = {};
+                let blockedCount = 0;
                 for (const [userId, userBlockedDevices] of Object.entries(blocked)) {
                     for (const [deviceId, device] of Object.entries(userBlockedDevices)) {
                         if (
@@ -335,13 +339,14 @@ MegolmEncryption.prototype._ensureOutboundSession = async function(
                             session.blockedDevicesNotified[userId][deviceId] === undefined
                         ) {
                             blockedMap[userId] = blockedMap[userId] || {};
-                            blockedMap[userId][deviceId] = {device};
+                            blockedMap[userId][deviceId] = { device };
+                            blockedCount++;
                         }
                     }
                 }
 
                 await this._notifyBlockedDevices(session, blockedMap);
-                logger.debug(`Notified blocked devices in ${this._roomId}`);
+                logger.debug(`Notified ${blockedCount} blocked devices in ${this._roomId}`);
             })(),
         ]);
     };
@@ -728,13 +733,18 @@ MegolmEncryption.prototype.reshareKeyWithDevice = async function(
 MegolmEncryption.prototype._shareKeyWithDevices = async function(
     session, key, payload, devicesByUser, errorDevices, otkTimeout, failedServers,
 ) {
+    logger.debug(`Ensuring Olm sessions for devices in ${this._roomId}`);
     const devicemap = await olmlib.ensureOlmSessionsForDevices(
         this._olmDevice, this._baseApis, devicesByUser, otkTimeout, failedServers,
+        logger.withPrefix(`[${this._roomId}]`),
     );
+    logger.debug(`Ensured Olm sessions for devices in ${this._roomId}`);
 
     this._getDevicesWithoutSessions(devicemap, devicesByUser, errorDevices);
 
+    logger.debug(`Sharing keys with Olm sessions in ${this._roomId}`);
     await this._shareKeyWithOlmSessions(session, key, payload, devicemap);
+    logger.debug(`Shared keys with Olm sessions in ${this._roomId}`);
 };
 
 MegolmEncryption.prototype._shareKeyWithOlmSessions = async function(
@@ -772,6 +782,11 @@ MegolmEncryption.prototype._shareKeyWithOlmSessions = async function(
 MegolmEncryption.prototype._notifyFailedOlmDevices = async function(
     session, key, failedDevices,
 ) {
+    logger.debug(
+        `Notifying ${failedDevices.length} devices we failed to ` +
+        `create Olm sessions in ${this._roomId}`,
+    );
+
     // mark the devices that failed as "handled" because we don't want to try
     // to claim a one-time-key for dead devices on every message.
     for (const {userId, deviceInfo} of failedDevices) {
@@ -786,6 +801,10 @@ MegolmEncryption.prototype._notifyFailedOlmDevices = async function(
           await this._olmDevice.filterOutNotifiedErrorDevices(
               failedDevices,
           );
+    logger.debug(
+        `Filtered down to ${filteredFailedDevices.length} error devices ` +
+        `in ${this._roomId}`,
+    );
     const blockedMap = {};
     for (const {userId, deviceInfo} of filteredFailedDevices) {
         blockedMap[userId] = blockedMap[userId] || {};
@@ -803,6 +822,10 @@ MegolmEncryption.prototype._notifyFailedOlmDevices = async function(
 
     // send the notifications
     await this._notifyBlockedDevices(session, blockedMap);
+    logger.debug(
+        `Notified ${filteredFailedDevices.length} devices we failed to ` +
+        `create Olm sessions in ${this._roomId}`,
+    );
 };
 
 /**
diff --git a/src/crypto/olmlib.js b/src/crypto/olmlib.js
index f55a9122e..eb0d8a4a9 100644
--- a/src/crypto/olmlib.js
+++ b/src/crypto/olmlib.js
@@ -183,18 +183,24 @@ export async function getExistingOlmSessions(
  * @param {Array} [failedServers] An array to fill with remote servers that
  *     failed to respond to one-time-key requests.
  *
+ * @param {Logger} [log] A possibly customised log
+ *
  * @return {Promise} resolves once the sessions are complete, to
  *    an Object mapping from userId to deviceId to
  *    {@link module:crypto~OlmSessionResult}
  */
 export async function ensureOlmSessionsForDevices(
-    olmDevice, baseApis, devicesByUser, force, otkTimeout, failedServers,
+    olmDevice, baseApis, devicesByUser, force, otkTimeout, failedServers, log,
 ) {
     if (typeof force === "number") {
+        log = failedServers;
         failedServers = otkTimeout;
         otkTimeout = force;
         force = false;
     }
+    if (!log) {
+        log = logger;
+    }
 
     const devicesWithoutSession = [
         // [userId, deviceId], ...
@@ -202,6 +208,39 @@ export async function ensureOlmSessionsForDevices(
     const result = {};
     const resolveSession = {};
 
+    // Mark all sessions this task intends to update as in progress. It is
+    // important to do this for all devices this task cares about in a single
+    // synchronous operation, as otherwise it is possible to have deadlocks
+    // where multiple tasks wait indefinitely on another task to update some set
+    // of common devices.
+    for (const [userId, devices] of Object.entries(devicesByUser)) {
+        for (const deviceInfo of devices) {
+            const deviceId = deviceInfo.deviceId;
+            const key = deviceInfo.getIdentityKey();
+
+            if (key === olmDevice.deviceCurve25519Key) {
+                // We don't start sessions with ourself, so there's no need to
+                // mark it in progress.
+                continue;
+            }
+
+            const forWhom = `for ${key} (${userId}:${deviceId})`;
+            if (!olmDevice._sessionsInProgress[key]) {
+                // pre-emptively mark the session as in-progress to avoid race
+                // conditions.  If we find that we already have a session, then
+                // we'll resolve
+                log.debug(`Marking Olm session in progress ${forWhom}`);
+                olmDevice._sessionsInProgress[key] = new Promise(resolve => {
+                    resolveSession[key] = (...args) => {
+                        log.debug(`Resolved Olm session in progress ${forWhom}`);
+                        delete olmDevice._sessionsInProgress[key];
+                        resolve(...args);
+                    };
+                });
+            }
+        }
+    }
+
     for (const [userId, devices] of Object.entries(devicesByUser)) {
         result[userId] = {};
         for (const deviceInfo of devices) {
@@ -216,7 +255,7 @@ export async function ensureOlmSessionsForDevices(
                 // new chain when this side has an active sender chain.
                 // If you see this message being logged in the wild, we should find
                 // the thing that is trying to send Olm messages to itself and fix it.
-                logger.info("Attempted to start session with ourself! Ignoring");
+                log.info("Attempted to start session with ourself! Ignoring");
                 // We must fill in the section in the return value though, as callers
                 // expect it to be there.
                 result[userId][deviceId] = {
@@ -226,41 +265,23 @@ export async function ensureOlmSessionsForDevices(
                 continue;
             }
 
-            if (!olmDevice._sessionsInProgress[key]) {
-                // pre-emptively mark the session as in-progress to avoid race
-                // conditions.  If we find that we already have a session, then
-                // we'll resolve
-                olmDevice._sessionsInProgress[key] = new Promise(
-                    (resolve, reject) => {
-                        resolveSession[key] = {
-                            resolve: (...args) => {
-                                delete olmDevice._sessionsInProgress[key];
-                                resolve(...args);
-                            },
-                            reject: (...args) => {
-                                delete olmDevice._sessionsInProgress[key];
-                                reject(...args);
-                            },
-                        };
-                    },
-                );
-            }
+            const forWhom = `for ${key} (${userId}:${deviceId})`;
+            log.debug(`Ensuring Olm session ${forWhom}`);
             const sessionId = await olmDevice.getSessionIdForDevice(
-                key, resolveSession[key],
+                key, resolveSession[key], log,
             );
+            log.debug(`Got Olm session ${sessionId} ${forWhom}`);
             if (sessionId !== null && resolveSession[key]) {
                 // we found a session, but we had marked the session as
-                // in-progress, so unmark it and unblock anything that was
-                // waiting
-                delete olmDevice._sessionsInProgress[key];
-                resolveSession[key].resolve();
-                delete resolveSession[key];
+                // in-progress, so resolve it now, which will unmark it and
+                // unblock anything that was waiting
+                resolveSession[key]();
             }
             if (sessionId === null || force) {
                 if (force) {
-                    logger.info("Forcing new Olm session for " + userId + ":" + deviceId);
+                    log.info(`Forcing new Olm session ${forWhom}`);
                 } else {
-                    logger.info("Making new Olm session for " + userId + ":" + deviceId);
+                    log.info(`Making new Olm session ${forWhom}`);
                 }
                 devicesWithoutSession.push([userId, deviceId]);
             }
@@ -283,20 +304,24 @@ export async function ensureOlmSessionsForDevices(
     // timeout on this request, let's first log whether that's the root
     // cause we're seeing in practice.
     // See also https://github.com/vector-im/element-web/issues/16194
-    const otkTimeoutLogger = setTimeout(() => {
-        logger.error(`Homeserver never replied while claiming ${taskDetail}`);
-    }, otkTimeout);
+    let otkTimeoutLogger;
+    // XXX: Perhaps there should be a default timeout?
+    if (otkTimeout) {
+        otkTimeoutLogger = setTimeout(() => {
+            log.error(`Homeserver never replied while claiming ${taskDetail}`);
+        }, otkTimeout);
+    }
     try {
-        logger.debug(`Claiming ${taskDetail}`);
+        log.debug(`Claiming ${taskDetail}`);
         res = await baseApis.claimOneTimeKeys(
             devicesWithoutSession, oneTimeKeyAlgorithm, otkTimeout,
         );
-        logger.debug(`Claimed ${taskDetail}`);
+        log.debug(`Claimed ${taskDetail}`);
     } catch (e) {
         for (const resolver of Object.values(resolveSession)) {
-            resolver.resolve();
+            resolver();
         }
-        logger.log(`Failed to claim ${taskDetail}`, e, devicesWithoutSession);
+        log.log(`Failed to claim ${taskDetail}`, e, devicesWithoutSession);
         throw e;
     } finally {
         clearTimeout(otkTimeoutLogger);
@@ -306,10 +331,10 @@ export async function ensureOlmSessionsForDevices(
         failedServers.push(...Object.keys(res.failures));
     }
 
-    const otk_res = res.one_time_keys || {};
+    const otkResult = res.one_time_keys || {};
     const promises = [];
     for (const [userId, devices] of Object.entries(devicesByUser)) {
-        const userRes = otk_res[userId] || {};
+        const userRes = otkResult[userId] || {};
         for (let j = 0; j < devices.length; j++) {
             const deviceInfo = devices[j];
             const deviceId = deviceInfo.deviceId;
@@ -336,11 +361,12 @@ export async function ensureOlmSessionsForDevices(
             }
 
             if (!oneTimeKey) {
-                const msg = "No one-time keys (alg=" + oneTimeKeyAlgorithm +
-                      ") for device " + userId + ":" + deviceId;
-                logger.warn(msg);
+                log.warn(
+                    `No one-time keys (alg=${oneTimeKeyAlgorithm}) ` +
+                    `for device ${userId}:${deviceId}`,
+                );
                 if (resolveSession[key]) {
-                    resolveSession[key].resolve();
+                    resolveSession[key]();
                 }
                 continue;
             }
@@ -350,12 +376,12 @@ export async function ensureOlmSessionsForDevices(
                     olmDevice, oneTimeKey, userId, deviceInfo,
                 ).then((sid) => {
                     if (resolveSession[key]) {
-                        resolveSession[key].resolve(sid);
+                        resolveSession[key](sid);
                     }
                     result[userId][deviceId].sessionId = sid;
                 }, (e) => {
                     if (resolveSession[key]) {
-                        resolveSession[key].resolve();
+                        resolveSession[key]();
                     }
                     throw e;
                 }),
@@ -364,9 +390,9 @@ export async function ensureOlmSessionsForDevices(
     }
 
     taskDetail = `Olm sessions for ${promises.length} devices`;
-    logger.debug(`Starting ${taskDetail}`);
+    log.debug(`Starting ${taskDetail}`);
     await Promise.all(promises);
-    logger.debug(`Started ${taskDetail}`);
+    log.debug(`Started ${taskDetail}`);
     return result;
 }
 
diff --git a/src/crypto/store/indexeddb-crypto-store-backend.js b/src/crypto/store/indexeddb-crypto-store-backend.js
index 505e5fe51..6ecffe7be 100644
--- a/src/crypto/store/indexeddb-crypto-store-backend.js
+++ b/src/crypto/store/indexeddb-crypto-store-backend.js
@@ -34,6 +34,7 @@ export class Backend {
      */
     constructor(db) {
         this._db = db;
+        this._nextTxnId = 0;
 
         // make sure we close the db on `onversionchange` - otherwise
         // attempts to delete the database will block (and subsequent
@@ -757,10 +758,21 @@ export class Backend {
         }));
     }
 
-    doTxn(mode, stores, func) {
+    doTxn(mode, stores, func, log = logger) {
+        const txnId = this._nextTxnId++;
+        const startTime = Date.now();
+        const description = `${mode} crypto store transaction ${txnId} in ${stores}`;
+        log.debug(`Starting ${description}`);
         const txn = this._db.transaction(stores, mode);
         const promise = promiseifyTxn(txn);
         const result = func(txn);
+        promise.then(() => {
+            const elapsedTime = Date.now() - startTime;
+            log.debug(`Finished ${description}, took ${elapsedTime} ms`);
+        }, () => {
+            const elapsedTime = Date.now() - startTime;
+            log.error(`Failed ${description}, took ${elapsedTime} ms`);
+        });
         return promise.then(() => {
             return result;
         });
diff --git a/src/crypto/store/indexeddb-crypto-store.js b/src/crypto/store/indexeddb-crypto-store.js
index 3dc49858c..50f3c2678 100644
--- a/src/crypto/store/indexeddb-crypto-store.js
+++ b/src/crypto/store/indexeddb-crypto-store.js
@@ -596,6 +596,7 @@ export class IndexedDBCryptoStore {
      * @param {function(*)} func Function called with the
      *     transaction object: an opaque object that should be passed
      *     to store functions.
+     * @param {Logger} [log] A possibly customised log
      * @return {Promise} Promise that resolves with the result of the `func`
      *     when the transaction is complete. If the backend is
      *     async (ie. the indexeddb backend) any of the callback
@@ -603,8 +604,8 @@ export class IndexedDBCryptoStore {
      *     reject with that exception. On synchronous backends, the
      *     exception will propagate to the caller of the getFoo method.
      */
-    doTxn(mode, stores, func) {
-        return this._backend.doTxn(mode, stores, func);
+    doTxn(mode, stores, func, log) {
+        return this._backend.doTxn(mode, stores, func, log);
     }
 }
 
diff --git a/src/logger.ts b/src/logger.ts
index fc5ceeb4d..e5fced726 100644
--- a/src/logger.ts
+++ b/src/logger.ts
@@ -1,6 +1,6 @@
 /*
 Copyright 2018 André Jaenisch
-Copyright 2019 The Matrix.org Foundation C.I.C.
+Copyright 2019, 2021 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -19,7 +19,7 @@ limitations under the License.
  * @module logger
  */
 
-import log from "loglevel";
+import log, { Logger } from "loglevel";
 
 // This is to demonstrate, that you can use any namespace you want.
 // Namespaces allow you to turn on/off the logging for specific parts of the
@@ -36,6 +36,11 @@ const DEFAULT_NAMESPACE = "matrix";
 // when logging so we always get the current value of console methods.
 log.methodFactory = function(methodName, logLevel, loggerName) {
     return function(...args) {
+        /* eslint-disable babel/no-invalid-this */
+        if (this.prefix) {
+            args.unshift(this.prefix);
+        }
+        /* eslint-enable babel/no-invalid-this */
         const supportedByConsole = methodName === "error" ||
             methodName === "warn" ||
             methodName === "trace" ||
@@ -54,6 +59,30 @@ log.methodFactory = function(methodName, logLevel, loggerName) {
  * Drop-in replacement for <code>console</code> using {@link https://www.npmjs.com/package/loglevel|loglevel}.
  * Can be tailored down to specific use cases if needed.
  */
-export const logger = log.getLogger(DEFAULT_NAMESPACE);
+export const logger: PrefixedLogger = log.getLogger(DEFAULT_NAMESPACE);
 logger.setLevel(log.levels.DEBUG);
 
+interface PrefixedLogger extends Logger {
+    withPrefix?: (prefix: string) => PrefixedLogger;
+    prefix?: string;
+}
+
+function extendLogger(logger: PrefixedLogger) {
+    logger.withPrefix = function(prefix: string): PrefixedLogger {
+        const existingPrefix = this.prefix || "";
+        return getPrefixedLogger(existingPrefix + prefix);
+    };
+}
+
+extendLogger(logger);
+
+function getPrefixedLogger(prefix): PrefixedLogger {
+    const prefixLogger: PrefixedLogger = log.getLogger(`${DEFAULT_NAMESPACE}-${prefix}`);
+    if (prefixLogger.prefix !== prefix) {
+        // Only do this setup work the first time through, as loggers are saved by name.
+        extendLogger(prefixLogger);
+        prefixLogger.prefix = prefix;
+        prefixLogger.setLevel(log.levels.DEBUG);
+    }
+    return prefixLogger;
+}
diff --git a/src/matrix.ts b/src/matrix.ts
index cffda610c..f1014c5de 100644
--- a/src/matrix.ts
+++ b/src/matrix.ts
@@ -52,7 +52,7 @@ export * from "./store/session/webstorage";
 export * from "./crypto/store/memory-crypto-store";
 export * from "./crypto/store/indexeddb-crypto-store";
 export * from "./content-repo";
-export const ContentHelpers = import("./content-helpers");
+export * as ContentHelpers from "./content-helpers";
 export {
     createNewMatrixCall,
     setAudioOutput as setMatrixCallAudioOutput,
diff --git a/src/models/room-member.js b/src/models/room-member.js
index 0ba6edd60..444c45609 100644
--- a/src/models/room-member.js
+++ b/src/models/room-member.js
@@ -290,6 +290,9 @@ RoomMember.prototype.getMxcAvatarUrl = function() {
     return null;
 };
 
+const MXID_PATTERN = /@.+:.+/;
+const LTR_RTL_PATTERN = /[\u200E\u200F\u202A-\u202F]/;
+
 function calculateDisplayName(selfUserId, displayName, roomState) {
     if (!displayName || displayName === selfUserId) {
         return selfUserId;
@@ -308,13 +311,13 @@ function calculateDisplayName(selfUserId, displayName, roomState) {
     // Next check if the name contains something that look like a mxid
     // If it does, it may be someone trying to impersonate someone else
     // Show full mxid in this case
-    let disambiguate = /@.+:.+/.test(displayName);
+    let disambiguate = MXID_PATTERN.test(displayName);
 
     if (!disambiguate) {
         // Also show mxid if the display name contains any LTR/RTL characters as these
         // make it very difficult for us to find similar *looking* display names
         // E.g "Mark" could be cloned by writing "kraM" but in RTL.
-        disambiguate = /[\u200E\u200F\u202A-\u202F]/.test(displayName);
+        disambiguate = LTR_RTL_PATTERN.test(displayName);
     }
 
     if (!disambiguate) {
diff --git a/src/models/room.js b/src/models/room.js
index 047d7c5f4..9c321e1bb 100644
--- a/src/models/room.js
+++ b/src/models/room.js
@@ -30,7 +30,7 @@ import {RoomMember} from "./room-member";
 import {RoomSummary} from "./room-summary";
 import {logger} from '../logger';
 import {ReEmitter} from '../ReEmitter';
-import {EventType} from "../@types/event";
+import {EventType, RoomCreateTypeField, RoomType} from "../@types/event";
 
 // These constants are used as sane defaults when the homeserver doesn't support
 // the m.room_versions capability. In practice, KNOWN_SAFE_ROOM_VERSION should be
@@ -1856,6 +1856,27 @@ Room.prototype.getJoinRule = function() {
     return this.currentState.getJoinRule();
 };
 
+/**
+ * Returns the type of the room from the `m.room.create` event content or undefined if none is set
+ * @returns {?string} the type of the room. Currently only RoomType.Space is known.
+ */
+Room.prototype.getType = function() {
+    const createEvent = this.currentState.getStateEvents("m.room.create", "");
+    if (!createEvent) {
+        logger.warn("Room " + this.roomId + " does not have an m.room.create event");
+        return undefined;
+    }
+    return createEvent.getContent()[RoomCreateTypeField];
+};
+
+/**
+ * Returns whether the room is a space-room as defined by MSC1772.
+ * @returns {boolean} true if the room's type is RoomType.Space
+ */
+Room.prototype.isSpaceRoom = function() {
+    return this.getType() === RoomType.Space;
+};
+
 /**
  * This is an internal method. Calculates the name of the room from the current
  * room state.
diff --git a/src/webrtc/call.ts b/src/webrtc/call.ts
index 2a74d3736..7e6de3cd8 100644
--- a/src/webrtc/call.ts
+++ b/src/webrtc/call.ts
@@ -257,8 +257,6 @@ export class MatrixCall extends EventEmitter {
     private localAVStream: MediaStream;
     private inviteOrAnswerSent: boolean;
     private waitForLocalAVStream: boolean;
-    // XXX: This is either the invite or answer from remote...
-    private msg: any;
     // XXX: I don't know why this is called 'config'.
     private config: MediaStreamConstraints;
     private successor: MatrixCall;
@@ -290,6 +288,11 @@ export class MatrixCall extends EventEmitter {
     private makingOffer: boolean;
     private ignoreOffer: boolean;
 
+    // If candidates arrive before we've picked an opponent (which, in particular,
+    // will happen if the opponent sends candidates eagerly before the user answers
+    // the call) we buffer them up here so we can then add the ones from the party we pick
+    private remoteCandidateBuffer = new Map<string, RTCIceCandidate[]>();
+
     constructor(opts: CallOpts) {
         super();
         this.roomId = opts.roomId;
@@ -297,9 +300,6 @@ export class MatrixCall extends EventEmitter {
         this.type = null;
         this.forceTURN = opts.forceTURN;
         this.ourPartyId = this.client.deviceId;
-        // We compare this to null to checks the presence of a party ID:
-        // make sure it's null, not undefined
-        this.opponentPartyId = null;
         // Array of Objects with urls, username, credential keys
         this.turnServers = opts.turnServers || [];
         if (this.turnServers.length === 0 && this.client.isFallbackICEServerAllowed()) {
@@ -524,11 +524,16 @@ export class MatrixCall extends EventEmitter {
      * @param {MatrixEvent} event The m.call.invite event
      */
     async initWithInvite(event: MatrixEvent) {
-        this.msg = event.getContent();
+        const invite = event.getContent();
         this.direction = CallDirection.Inbound;
+
         this.peerConn = this.createPeerConnection();
+        // we must set the party ID before await-ing on anything: the call event
+        // handler will start giving us more call events (eg. candidates) so if
+        // we haven't set the party ID, we'll ignore them.
+        this.chooseOpponent(event);
         try {
-            await this.peerConn.setRemoteDescription(this.msg.offer);
+            await this.peerConn.setRemoteDescription(invite.offer);
         } catch (e) {
             logger.debug("Failed to set remote description", e);
             this.terminate(CallParty.Local, CallErrorCode.SetRemoteDescription, false);
@@ -547,13 +552,6 @@ export class MatrixCall extends EventEmitter {
         this.type = this.remoteStream.getTracks().some(t => t.kind === 'video') ? CallType.Video : CallType.Voice;
 
         this.setState(CallState.Ringing);
-        this.opponentVersion = this.msg.version;
-        if (this.opponentVersion !== 0) {
-            // ignore party ID in v0 calls: party ID isn't a thing until v1
-            this.opponentPartyId = this.msg.party_id || null;
-        }
-        this.opponentCaps = this.msg.capabilities || {};
-        this.opponentMember = event.sender;
 
         if (event.getLocalAge()) {
             setTimeout(() => {
@@ -567,7 +565,7 @@ export class MatrixCall extends EventEmitter {
                     }
                     this.emit(CallEvent.Hangup);
                 }
-            }, this.msg.lifetime - event.getLocalAge());
+            }, invite.lifetime - event.getLocalAge());
         }
     }
 
@@ -579,7 +577,6 @@ export class MatrixCall extends EventEmitter {
         // perverse as it may seem, sometimes we want to instantiate a call with a
         // hangup message (because when getting the state of the room on load, events
         // come in reverse order and we want to remember that a call has been hung up)
-        this.msg = event.getContent();
         this.setState(CallState.Ended);
     }
 
@@ -873,7 +870,7 @@ export class MatrixCall extends EventEmitter {
         // Now we wait for the negotiationneeded event
     };
 
-    private sendAnswer() {
+    private async sendAnswer() {
         const answerContent = {
             answer: {
                 sdp: this.peerConn.localDescription.sdp,
@@ -895,12 +892,12 @@ export class MatrixCall extends EventEmitter {
         logger.info(`Discarding ${this.candidateSendQueue.length} candidates that will be sent in answer`);
         this.candidateSendQueue = [];
 
-        this.sendVoipEvent(EventType.CallAnswer, answerContent).then(() => {
+        try {
+            await this.sendVoipEvent(EventType.CallAnswer, answerContent);
             // If this isn't the first time we've tried to send the answer,
             // we may have candidates queued up, so send them now.
             this.inviteOrAnswerSent = true;
-            this.sendCandidateQueue();
-        }).catch((error) => {
+        } catch (error) {
             // We've failed to answer: back to the ringing state
             this.setState(CallState.Ringing);
             this.client.cancelPendingEvent(error.event);
@@ -913,7 +910,11 @@ export class MatrixCall extends EventEmitter {
             }
             this.emit(CallEvent.Error, new CallError(code, message, error));
             throw error;
-        });
+        }
+
+        // error handler re-throws so this won't happen on error, but
+        // we don't want the same error handling on the candidate queue
+        this.sendCandidateQueue();
     }
 
     private gotUserMediaForAnswer = async (stream: MediaStream) => {
@@ -1017,37 +1018,33 @@ export class MatrixCall extends EventEmitter {
             return;
         }
 
-        if (!this.partyIdMatches(ev.getContent())) {
-            logger.info(
-                `Ignoring candidates from party ID ${ev.getContent().party_id}: ` +
-                `we have chosen party ID ${this.opponentPartyId}`,
-            );
-            return;
-        }
-
         const cands = ev.getContent().candidates;
         if (!cands) {
             logger.info("Ignoring candidates event with no candidates!");
             return;
         }
 
-        for (const cand of cands) {
-            if (
-                (cand.sdpMid === null || cand.sdpMid === undefined) &&
-                (cand.sdpMLineIndex === null || cand.sdpMLineIndex === undefined)
-            ) {
-                logger.debug("Ignoring remote ICE candidate with no sdpMid or sdpMLineIndex");
-                return;
-            }
-            logger.debug("Got remote ICE " + cand.sdpMid + " candidate: " + cand.candidate);
-            try {
-                this.peerConn.addIceCandidate(cand);
-            } catch (err) {
-                if (!this.ignoreOffer) {
-                    logger.info("Failed to add remore ICE candidate", err);
-                }
-            }
+        const fromPartyId = ev.getContent().version === 0 ? null : ev.getContent().party_id || null;
+
+        if (this.opponentPartyId === undefined) {
+            // we haven't picked an opponent yet so save the candidates
+            logger.info(`Bufferring ${cands.length} candidates until we pick an opponent`);
+            const bufferedCands = this.remoteCandidateBuffer.get(fromPartyId) || [];
+            bufferedCands.push(...cands);
+            this.remoteCandidateBuffer.set(fromPartyId, bufferedCands);
+            return;
         }
+
+        if (!this.partyIdMatches(ev.getContent())) {
+            logger.info(
+                `Ignoring candidates from party ID ${ev.getContent().party_id}: ` +
+                `we have chosen party ID ${this.opponentPartyId}`,
+            );
+
+            return;
+        }
+
+        this.addIceCandidates(cands);
     }
 
     /**
@@ -1059,7 +1056,7 @@ export class MatrixCall extends EventEmitter {
             return;
         }
 
-        if (this.opponentPartyId !== null) {
+        if (this.opponentPartyId !== undefined) {
             logger.info(
                 `Ignoring answer from party ID ${event.getContent().party_id}: ` +
                 `we already have an answer/reject from ${this.opponentPartyId}`,
@@ -1067,12 +1064,7 @@ export class MatrixCall extends EventEmitter {
             return;
         }
 
-        this.opponentVersion = event.getContent().version;
-        if (this.opponentVersion !== 0) {
-            this.opponentPartyId = event.getContent().party_id || null;
-        }
-        this.opponentCaps = event.getContent().capabilities || {};
-        this.opponentMember = event.sender;
+        this.chooseOpponent(event);
 
         this.setState(CallState.Connecting);
 
@@ -1247,19 +1239,9 @@ export class MatrixCall extends EventEmitter {
 
         try {
             await this.sendVoipEvent(eventType, content);
-            this.sendCandidateQueue();
-            if (this.state === CallState.CreateOffer) {
-                this.inviteOrAnswerSent = true;
-                this.setState(CallState.InviteSent);
-                this.inviteTimeout = setTimeout(() => {
-                    this.inviteTimeout = null;
-                    if (this.state === CallState.InviteSent) {
-                        this.hangup(CallErrorCode.InviteTimeout, false);
-                    }
-                }, CALL_TIMEOUT_MS);
-            }
         } catch (error) {
-            this.client.cancelPendingEvent(error.event);
+            logger.error("Failed to send invite", error);
+            if (error.event) this.client.cancelPendingEvent(error.event);
 
             let code = CallErrorCode.SignallingFailed;
             let message = "Signalling failed";
@@ -1274,6 +1256,22 @@ export class MatrixCall extends EventEmitter {
 
             this.emit(CallEvent.Error, new CallError(code, message, error));
             this.terminate(CallParty.Local, code, false);
+
+            // no need to carry on & send the candidate queue, but we also
+            // don't want to rethrow the error
+            return;
+        }
+
+        this.sendCandidateQueue();
+        if (this.state === CallState.CreateOffer) {
+            this.inviteOrAnswerSent = true;
+            this.setState(CallState.InviteSent);
+            this.inviteTimeout = setTimeout(() => {
+                this.inviteTimeout = null;
+                if (this.state === CallState.InviteSent) {
+                    this.hangup(CallErrorCode.InviteTimeout, false);
+                }
+            }, CALL_TIMEOUT_MS);
         }
     };
 
@@ -1610,7 +1608,7 @@ export class MatrixCall extends EventEmitter {
         }
     }
 
-    private sendCandidateQueue() {
+    private async sendCandidateQueue() {
         if (this.candidateSendQueue.length === 0) {
             return;
         }
@@ -1622,20 +1620,28 @@ export class MatrixCall extends EventEmitter {
             candidates: cands,
         };
         logger.debug("Attempting to send " + cands.length + " candidates");
-        this.sendVoipEvent(EventType.CallCandidates, content).then(() => {
-            this.candidateSendTries = 0;
-            this.sendCandidateQueue();
-        }, (error) => {
-            for (let i = 0; i < cands.length; i++) {
-                this.candidateSendQueue.push(cands[i]);
-            }
+        try {
+            await this.sendVoipEvent(EventType.CallCandidates, content);
+        } catch (error) {
+            // don't retry this event: we'll send another one later as we might
+            // have more candidates by then.
+            if (error.event) this.client.cancelPendingEvent(error.event);
+
+            // put all the candidates we failed to send back in the queue
+            this.candidateSendQueue.push(...cands);
 
             if (this.candidateSendTries > 5) {
                 logger.debug(
                     "Failed to send candidates on attempt " + this.candidateSendTries +
-                    ". Giving up for now.", error,
+                    ". Giving up on this call.", error,
                 );
-                this.candidateSendTries = 0;
+
+                const code = CallErrorCode.SignallingFailed;
+                const message = "Signalling failed";
+
+                this.emit(CallEvent.Error, new CallError(code, message, error));
+                this.hangup(code, false);
+
                 return;
             }
 
@@ -1645,7 +1651,7 @@ export class MatrixCall extends EventEmitter {
             setTimeout(() => {
                 this.sendCandidateQueue();
             }, delayMs);
-        });
+        }
     }
 
     private async placeCallWithConstraints(constraints: MediaStreamConstraints) {
@@ -1689,9 +1695,60 @@ export class MatrixCall extends EventEmitter {
 
     private partyIdMatches(msg): boolean {
         // They must either match or both be absent (in which case opponentPartyId will be null)
-        const msgPartyId = msg.party_id || null;
+        // Also we ignore party IDs on the invite/offer if the version is 0, so we must do the same
+        // here and use null if the version is 0 (woe betide any opponent sending messages in the
+        // same call with different versions)
+        const msgPartyId = msg.version === 0 ? null : msg.party_id || null;
         return msgPartyId === this.opponentPartyId;
     }
+
+    // Commits to an opponent for the call
+    // ev: An invite or answer event
+    private chooseOpponent(ev: MatrixEvent) {
+        // I choo-choo-choose you
+        const msg = ev.getContent();
+
+        this.opponentVersion = msg.version;
+        if (this.opponentVersion === 0) {
+            // set to null to indicate that we've chosen an opponent, but because
+            // they're v0 they have no party ID (even if they sent one, we're ignoring it)
+            this.opponentPartyId = null;
+        } else {
+            // set to their party ID, or if they're naughty and didn't send one despite
+            // not being v0, set it to null to indicate we picked an opponent with no
+            // party ID
+            this.opponentPartyId = msg.party_id || null;
+        }
+        this.opponentCaps = msg.capabilities || {};
+        this.opponentMember = ev.sender;
+
+        const bufferedCands = this.remoteCandidateBuffer.get(this.opponentPartyId);
+        if (bufferedCands) {
+            logger.info(`Adding ${bufferedCands.length} buffered candidates for opponent ${this.opponentPartyId}`);
+            this.addIceCandidates(bufferedCands);
+        }
+        this.remoteCandidateBuffer = null;
+    }
+
+    private addIceCandidates(cands: RTCIceCandidate[]) {
+        for (const cand of cands) {
+            if (
+                (cand.sdpMid === null || cand.sdpMid === undefined) &&
+                (cand.sdpMLineIndex === null || cand.sdpMLineIndex === undefined)
+            ) {
+                logger.debug("Ignoring remote ICE candidate with no sdpMid or sdpMLineIndex");
+                return;
+            }
+            logger.debug("Got remote ICE " + cand.sdpMid + " candidate: " + cand.candidate);
+            try {
+                this.peerConn.addIceCandidate(cand);
+            } catch (err) {
+                if (!this.ignoreOffer) {
+                    logger.info("Failed to add remore ICE candidate", err);
+                }
+            }
+        }
+    }
 }
 
 function setTracksEnabled(tracks: Array<MediaStreamTrack>, enabled: boolean) {
diff --git a/src/webrtc/callEventHandler.ts b/src/webrtc/callEventHandler.ts
index ba4452ea8..304eacfdd 100644
--- a/src/webrtc/callEventHandler.ts
+++ b/src/webrtc/callEventHandler.ts
@@ -138,6 +138,8 @@ export class CallEventHandler {
                 );
             }
 
+            const timeUntilTurnCresExpire = this.client.getTurnServersExpiry() - Date.now();
+            logger.info("Current turn creds expire in " + timeUntilTurnCresExpire + " seconds");
             call = createNewMatrixCall(this.client, event.getRoomId(), {
                 forceTURN: this.client._forceTURN,
             });
diff --git a/yarn.lock b/yarn.lock
index a47f6eb4e..d3a09a364 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -5069,11 +5069,16 @@ lodash.sortby@^4.7.0:
   resolved "https://registry.yarnpkg.com/lodash.sortby/-/lodash.sortby-4.7.0.tgz#edd14c824e2cc9c1e0b0a1b42bb5210516a42438"
   integrity sha1-7dFMgk4sycHgsKG0K7UhBRakJDg=
 
-lodash@^4.17.14, lodash@^4.17.15, lodash@^4.17.19, lodash@^4.17.20, lodash@^4.17.4:
+lodash@^4.17.14, lodash@^4.17.15, lodash@^4.17.19, lodash@^4.17.20:
   version "4.17.20"
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.20.tgz#b44a9b6297bcb698f1c51a3545a2b3b368d59c52"
   integrity sha512-PlhdFcillOINfeV7Ni6oF1TAEayyZBoZ8bcshTHqOYJYlrqzRK5hagpagky5o4HfCzzd1TRkXPMFq6cKk9rGmA==
 
+lodash@^4.17.4:
+  version "4.17.21"
+  resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.21.tgz#679591c564c3bffaae8454cf0b3df370c3d6911c"
+  integrity sha512-v2kDEe57lecTulaDIuNTPy3Ry4gLGJ6Z1O3vE1krgXZNrsQ+LFTGHVxVjcXPs17LhbZVGedAJv8XZ1tvj5FvSg==
+
 loglevel@^1.7.1:
   version "1.7.1"
   resolved "https://registry.yarnpkg.com/loglevel/-/loglevel-1.7.1.tgz#005fde2f5e6e47068f935ff28573e125ef72f197"
@@ -5917,9 +5922,9 @@ pug-attrs@^2.0.4:
     pug-runtime "^2.0.5"
 
 pug-code-gen@^2.0.2:
-  version "2.0.2"
-  resolved "https://registry.yarnpkg.com/pug-code-gen/-/pug-code-gen-2.0.2.tgz#ad0967162aea077dcf787838d94ed14acb0217c2"
-  integrity sha512-kROFWv/AHx/9CRgoGJeRSm+4mLWchbgpRzTEn8XCiwwOy6Vh0gAClS8Vh5TEJ9DBjaP8wCjS3J6HKsEsYdvaCw==
+  version "2.0.3"
+  resolved "https://registry.yarnpkg.com/pug-code-gen/-/pug-code-gen-2.0.3.tgz#122eb9ada9b5bf601705fe15aaa0a7d26bc134ab"
+  integrity sha512-r9sezXdDuZJfW9J91TN/2LFbiqDhmltTFmGpHTsGdrNGp3p4SxAjjXEfnuK2e4ywYsRIVP0NeLbSAMHUcaX1EA==
   dependencies:
     constantinople "^3.1.2"
     doctypes "^1.1.0"