diff --git a/nobilis b/nobilis
index ace4fd7..3e522af 160000
--- a/nobilis
+++ b/nobilis
@@ -1 +1 @@
-Subproject commit ace4fd7a0cb579f5c4c6cfd3e21554b91ea6a9e8
+Subproject commit 3e522afdc55be5650fc260675026dc89acca9e73
diff --git a/src/renderer/src/app.css b/src/renderer/src/app.css
index 6041c3e..5a650f9 100644
--- a/src/renderer/src/app.css
+++ b/src/renderer/src/app.css
@@ -6675,3 +6675,53 @@ video.lightbox-media {
 .follow-button.following {
   color: var(--error);
 }
+
+/* --- Message source --------------------------------------------------- */
+
+/* The event behind a message, for when what is on screen is wrong. Built like
+   the prompts beside it and capped well short of the window: an event from a
+   bridge runs to hundreds of lines, and a dialog as tall as the conversation
+   behind it has its close button off screen. */
+.event-source {
+  display: flex;
+  flex-direction: column;
+  gap: var(--spacing-s);
+  width: min(680px, 90vw);
+  max-height: calc(100vh - 96px);
+  margin: auto;
+  padding: var(--spacing-m);
+  border: 1px solid var(--outline-medium);
+  border-radius: var(--corner-radius);
+  background: var(--surface-container-high);
+  box-shadow: 0 12px 40px rgba(0, 0, 0, 0.5);
+  overflow-y: auto;
+}
+
+.event-source-block {
+  display: flex;
+  flex-direction: column;
+  gap: var(--spacing-xs);
+}
+
+.event-source-label {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+}
+
+.event-source-json {
+  margin: 0;
+  max-height: 40vh;
+  padding: var(--spacing-s);
+  border: 1px solid var(--outline-medium);
+  border-radius: var(--corner-radius-small);
+  background: var(--surface-container-lowest);
+  color: var(--surface-variant-text);
+  font-family: var(--font-mono);
+  font-size: 0.78rem;
+  line-height: 1.45;
+  /* Both axes in its own box: JSON has long lines, and wrapping them would
+     destroy the indentation that makes it readable at all. */
+  overflow: auto;
+  white-space: pre;
+}
diff --git a/src/renderer/src/components/EventSource.tsx b/src/renderer/src/components/EventSource.tsx
new file mode 100644
index 0000000..c4ee0f5
--- /dev/null
+++ b/src/renderer/src/components/EventSource.tsx
@@ -0,0 +1,124 @@
+import { useEffect, useState } from 'react'
+import { createPortal } from 'react-dom'
+import { Icon, IconButton } from './Icon'
+import { useStore } from '../state/hooks'
+
+/** What the daemon read back off the server. */
+interface Source {
+  eventId: string
+  roomId: string
+  event: unknown
+  /** Present only where there was something to decrypt. */
+  decrypted?: unknown
+}
+
+/**
+ * The event behind a message, as the server holds it.
+ *
+ * What somebody reaches for when a message is wrong: a body that rendered
+ * oddly, a reply pointing at nothing, a state change nobody made. Everything
+ * else in this window shows what the client *made* of an event, and the whole
+ * reason to look at the source is that what it made may be wrong - so this is
+ * fetched from the server rather than taken from the timeline.
+ *
+ * Two halves in an encrypted room, which is what Element shows and what is
+ * actually useful: the envelope is what was sent and what any other client
+ * sees, and the plaintext is what it turned out to say. A room with nothing
+ * to decrypt shows one, because the same JSON twice teaches nobody anything.
+ */
+export function EventSource({
+  bufferId,
+  messageId,
+  onClose
+}: {
+  bufferId: string
+  messageId: string
+  onClose: () => void
+}): JSX.Element {
+  const store = useStore()
+  const [source, setSource] = useState<Source | null>(null)
+  const [failed, setFailed] = useState<string | null>(null)
+
+  useEffect(() => {
+    void window.moho
+      .rpc<Source>('matrixEventSource', { bufferId, messageId })
+      .then(setSource)
+      .catch((e: Error) => setFailed(e.message))
+  }, [bufferId, messageId])
+
+  // Escape closes it, the same as every other dialog here. A panel of JSON is
+  // exactly the thing somebody opens by accident and wants gone.
+  useEffect(() => {
+    const key = (e: KeyboardEvent): void => {
+      if (e.key === 'Escape') onClose()
+    }
+    window.addEventListener('keydown', key)
+    return () => window.removeEventListener('keydown', key)
+  }, [onClose])
+
+  const copy = (value: unknown): void => {
+    void window.moho.copyText(JSON.stringify(value, null, 2))
+    store.toast('info', 'Copied')
+  }
+
+  return createPortal(
+    <div className="lightbox-backdrop" onClick={onClose}>
+      <div className="event-source" onClick={(e) => e.stopPropagation()} role="dialog" aria-modal="true">
+        <div className="reason-prompt-head">
+          <Icon name="data_object" size={18} />
+          <span>Message source</span>
+        </div>
+        <div className="small muted ellipsis">{messageId}</div>
+
+        {!source && !failed && <div className="small muted">Reading…</div>}
+        {failed && <div className="small muted">Couldn’t read it: {failed}</div>}
+
+        {source && (
+          <>
+            {/* The plaintext first where there is one: it is the half that
+                answers the question, and the envelope below it is the
+                supporting evidence. */}
+            {source.decrypted !== undefined && source.decrypted !== null && (
+              <Block label="Decrypted" value={source.decrypted} onCopy={copy} />
+            )}
+            <Block
+              label={source.decrypted ? 'As sent (encrypted)' : 'As sent'}
+              value={source.event}
+              onCopy={copy}
+            />
+          </>
+        )}
+
+        <div className="reason-prompt-actions">
+          <button type="button" className="button" onClick={onClose}>
+            Close
+          </button>
+        </div>
+      </div>
+    </div>,
+    document.body
+  )
+}
+
+function Block({
+  label,
+  value,
+  onCopy
+}: {
+  label: string
+  value: unknown
+  onCopy: (value: unknown) => void
+}): JSX.Element {
+  return (
+    <div className="event-source-block">
+      <div className="event-source-label">
+        <span className="small muted">{label}</span>
+        <IconButton name="content_copy" size={16} title="Copy this" onClick={() => onCopy(value)} />
+      </div>
+      {/* Scrolls in its own box rather than stretching the dialog. An event
+          from a bridge can be hundreds of lines, and a dialog as tall as the
+          conversation behind it has no close button on screen. */}
+      <pre className="event-source-json">{JSON.stringify(value, null, 2)}</pre>
+    </div>
+  )
+}
diff --git a/src/renderer/src/components/MessageRow.tsx b/src/renderer/src/components/MessageRow.tsx
index a016108..0f3064a 100644
--- a/src/renderer/src/components/MessageRow.tsx
+++ b/src/renderer/src/components/MessageRow.tsx
@@ -3,6 +3,7 @@ import { createPortal } from 'react-dom'
 import { Icon } from './Icon'
 import { Avatar } from './Avatar'
 import { ReasonPrompt } from './ReasonPrompt'
+import { EventSource } from './EventSource'
 import { ForwardPicker } from './ForwardPicker'
 import { ContextMenu, useContextMenu, type MenuEntry } from './ContextMenu'
 import { MediaEmbed } from './MediaEmbed'
@@ -318,6 +319,7 @@ function MessageRowBody({
   const [pickerOpen, setPickerOpen] = useState(false)
   /** Writing the reason for a report, before it is sent. */
   const [reporting, setReporting] = useState(false)
+  const [sourceOpen, setSourceOpen] = useState(false)
   /** Choosing where to send this message on to. */
   const [forwarding, setForwarding] = useState(false)
   const reactButtonRef = useRef<HTMLButtonElement>(null)
@@ -564,6 +566,29 @@ function MessageRowBody({
           }
         ] as MenuEntry[])
       : []),
+    // The two things somebody reaches for when a message is wrong: an
+    // address to quote it by, and what it actually says. A permalink is how
+    // a message is shown to somebody outside the room, and the source is how
+    // a malformed event is described to whoever can fix it - without either,
+    // a bug in a room can only be described in prose.
+    ...(service === 'matrix' && !isSystem && message.id
+      ? ([
+          {
+            label: 'Copy link to this message',
+            icon: 'link',
+            onClick: () => {
+              void window.moho
+                .rpc<{ url: string }>('matrixMessageLink', { bufferId, messageId: message.id })
+                .then(({ url }) => {
+                  void window.moho.copyText(url)
+                  store.toast('info', 'Link copied')
+                })
+                .catch((e: Error) => store.toast('error', e.message))
+            }
+          },
+          { label: 'View source', icon: 'data_object', onClick: () => setSourceOpen(true) }
+        ] as MenuEntry[])
+      : []),
     ...(message.failed
       ? ([{ label: 'Retry', icon: 'refresh', onClick: () => store.retrySend(message.id) }] as MenuEntry[])
       : [])
@@ -1041,6 +1066,9 @@ function MessageRowBody({
           onClose={() => setForwarding(false)}
         />
       )}
+      {sourceOpen && (
+        <EventSource bufferId={bufferId} messageId={message.id} onClose={() => setSourceOpen(false)} />
+      )}
       {reporting && (
         <ReasonPrompt
           title={`Report ${message.from}’s message`}