diff --git a/main.go b/main.go
index 96f08aa..b44319e 100644
--- a/main.go
+++ b/main.go
@@ -132,6 +132,7 @@ func main() { // {{{
 	http.HandleFunc("/notes2", pageNotes2)
 	http.HandleFunc("/login", pageLogin)
 	http.HandleFunc("/sync", pageSync)
+	http.HandleFunc("/offline", pageOffline)
 
 	http.HandleFunc("/user/authenticate", AuthManager.AuthenticationHandler)
 
@@ -226,6 +227,15 @@ func pageServiceWorker(w http.ResponseWriter, r *http.Request) { // {{{
 		return
 	}
 } // }}}
+func pageOffline(w http.ResponseWriter, r *http.Request) { // {{{
+	page := NewPage("offline")
+
+	err := Webengine.Render(page, w, r)
+	if err != nil {
+		w.Write([]byte(err.Error()))
+		return
+	}
+} // }}}
 func pageLogin(w http.ResponseWriter, r *http.Request) { // {{{
 	page := NewPage("login")
 
diff --git a/static/js/node.mjs b/static/js/node.mjs
index 339016d..c4b2be0 100644
--- a/static/js/node.mjs
+++ b/static/js/node.mjs
@@ -85,7 +85,7 @@ export class N2NodeUI extends CustomHTMLElement {
 		// No point in showing markdown if there is no data.
 		// If there is no data, it will show a blank page regardless, and the user will most
 		// likely want to edit content, which can't be done in markdown.
-		const show = this.node.content().trim() !== '' && state
+		const show = this.node?.content().trim() !== '' && state
 
 		switch (show) {
 			case true:
diff --git a/static/service_worker.js b/static/service_worker.js
index c48c162..6c2e8e2 100644
--- a/static/service_worker.js
+++ b/static/service_worker.js
@@ -2,27 +2,41 @@ const CACHE_NAME = 'notes2-{{ .VERSION }}'
 const CACHED_ASSETS = [
 	'/',
 	'/notes2',
+	'/offline',
 
 	'/css/{{ .VERSION }}/main.css',
+	'/css/{{ .VERSION }}/markdown.css',
 	'/css/{{ .VERSION }}/notes2.css',
+	'/css/{{ .VERSION }}/theme.css',
 
-	'/js/{{ .VERSION }}/lib/fullcalendar.min.js',
-	'/js/{{ .VERSION }}/lib/node_modules/marked/marked.min.js',
-	'/js/{{ .VERSION }}/lib/sjcl.js',
+	'/images/{{ .VERSION }}/collapsed.svg',
+	'/images/{{ .VERSION }}/expanded.svg',
+	'/images/{{ .VERSION }}/icon_markdown_hollow.svg',
+	'/images/{{ .VERSION }}/icon_markdown.svg',
+	'/images/{{ .VERSION }}/icon_refresh.svg',
+	'/images/{{ .VERSION }}/icon_save_disabled.svg',
+	'/images/{{ .VERSION }}/icon_search.svg',
+	'/images/{{ .VERSION }}/leaf.svg',
+	'/images/{{ .VERSION }}/logo.svg',
 
 	'/js/{{ .VERSION }}/api.mjs',
+	'/js/{{ .VERSION }}/app.mjs',
+	'/js/{{ .VERSION }}/checklist.mjs',
+	'/js/{{ .VERSION }}/crypto.mjs',
+	'/js/{{ .VERSION }}/key.mjs',
+	'/js/{{ .VERSION }}/lib/custom_html_element.mjs',
+	'/js/{{ .VERSION }}/lib/fullcalendar.min.js',
+	'/js/{{ .VERSION }}/lib/node_modules/marked/lib/marked.esm.js',
+	'/js/{{ .VERSION }}/lib/node_modules/marked/marked.min.js',
+	'/js/{{ .VERSION }}/lib/node_modules/marked-token-position/lib/index.esm.js',
+	'/js/{{ .VERSION }}/lib/sjcl.js',
+	'/js/{{ .VERSION }}/marked_position.mjs',
+	'/js/{{ .VERSION }}/mbus.mjs',
 	'/js/{{ .VERSION }}/node.mjs',
 	'/js/{{ .VERSION }}/node_store.mjs',
 	'/js/{{ .VERSION }}/notes2.mjs',
 	'/js/{{ .VERSION }}/sync.mjs',
-	'/js/{{ .VERSION }}/key.mjs',
-	'/js/{{ .VERSION }}/crypto.mjs',
-	'/js/{{ .VERSION }}/checklist.mjs',
-
-	'/images/{{ .VERSION }}/logo.svg',
-	'/images/{{ .VERSION }}/leaf.svg',
-	'/images/{{ .VERSION }}/collapsed.svg',
-	'/images/{{ .VERSION }}/expanded.svg',
+	'/js/{{ .VERSION }}/tree.mjs',
 ]
 
 async function precache() {
@@ -32,13 +46,50 @@ async function precache() {
 
 async function fetchAsset(event) {
 	try {
-		return await fetch(event.request)
-	} catch (e) {
 		const cache = await caches.open(CACHE_NAME)
-		return cache.match(event.request)
+		const match = await cache.match(event.request)
+
+		if (match !== undefined) {
+			// -----------------------------------------------
+			// This page is precached - return it immediately.
+			// -----------------------------------------------
+			//console.log('From cache', event.request.url)
+			return match
+		} else {
+			// ---------------------------------------------------------------
+			// Not in cache - send it for an online request/browser cache hit.
+			// ---------------------------------------------------------------
+			console.log('From network', event.request.url)
+			const resp = await fetch(event.request)
+
+			// This will trigger on an HTTP error such as 502.
+			if (!resp.ok) {
+				console.log('HTTP error', resp.status)
+
+				// When JSON is expected, return that instead of the offline HTML page.
+				return await offline(event, `${resp.status} ${resp.statusText}`)
+			}
+			return resp
+		}
+	} catch (e) {
+		// An error here is something like a DNS problem, not a regular HTTP problem.
+		console.log('Network error', e, event.request.url)
+		return await offline(event, e)
 	}
 }
 
+async function offline(event, errText) {
+	if (event.request.headers.get('X-JSON')) {
+		return new Response('{ "OK": false, "Error": "Network is offline"}', { headers: { 'Content-Type': 'application/json' } })
+	}
+
+	const cache = await caches.open(CACHE_NAME)
+	const offline = await cache.match('/offline')
+	let body = await offline.text()
+	body = body.replace('||ERROR||', errText)
+	return new Response(body, { headers: { 'Content-Type': 'text/html' } })
+}
+
 async function cleanupCache() {
 	const keys = await caches.keys()
 	const keysToDelete = keys.map(key => {
@@ -61,6 +112,6 @@ self.addEventListener('activate', event => {
 })
 
 self.addEventListener('fetch', event => {
-	//console.log('SERVICE WORKER: fetch')
+	//console.log('SERVICE WORKER: fetch', event.request.url)
 	event.respondWith(fetchAsset(event))
 })
diff --git a/views/pages/offline.gotmpl b/views/pages/offline.gotmpl
new file mode 100644
index 0000000..0c283f9
--- /dev/null
+++ b/views/pages/offline.gotmpl
@@ -0,0 +1,4 @@
+{{ define "page" }}
+<div>Site is offline.</div>
+<div>||ERROR||</div>
+{{ end }}