diff --git a/lib/index.js b/lib/index.js
index 859b61e..8bdfbd8 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -7,11 +7,12 @@ const b4a = require('b4a')
 
 /**
  * @typedef {ReturnType<import('ppppp-db').init>} PPPPPDB
+ * @typedef {ReturnType<import('ppppp-set').init>} PPPPPSet
  * @typedef {import('ppppp-db/msg-v4').AccountAdd} AccountAdd
  * @typedef {Buffer | Uint8Array} B4A
  * @typedef {{global: {path: string}}} ExpectedConfig
  * @typedef {{global: {path?: string}}} Config
- * @typedef {{type: 'follow'}} FollowPromise
+ * @typedef {{type: 'follow', account: string}} FollowPromise
  * @typedef {{type: 'account-add', account: string}} AccountAddPromise
  * @typedef {FollowPromise | AccountAddPromise} PPromise
  */
@@ -30,6 +31,15 @@ function assertDBPlugin(peer) {
   if (!peer.db) throw new Error('promise plugin plugin requires ppppp-db plugin')
 }
 
+/**
+ * @param {{ set: PPPPPSet | null }} peer
+ * @returns {asserts peer is { set: PPPPPSet }}
+ */
+function assertSetPlugin(peer) {
+  // prettier-ignore
+  if (!peer.set) throw new Error('promise plugin plugin requires ppppp-set plugin')
+}
+
 /**
  * @param {Config} config
  * @returns {asserts config is ExpectedConfig}
@@ -57,7 +67,7 @@ module.exports = {
   },
 
   /**
-   * @param {{ db: PPPPPDB | null }} peer
+   * @param {{ db: PPPPPDB | null; set: PPPPPSet | null }} peer
    * @param {Config} config
    */
   init(peer, config) {
@@ -98,19 +108,21 @@ module.exports = {
      * @return {Error | null}
      */
     function validatePromise(promise) {
-      if (
-        typeof promise !== 'object' ||
-        typeof promise.type !== 'string' ||
-        (promise.type !== 'follow' && promise.type !== 'account-add')
-      ) {
+      if (typeof promise !== 'object' || typeof promise.type !== 'string') {
         return Error('Invalid promise created: ' + JSON.stringify(promise))
       }
-      if (
-        promise.type === 'account-add' &&
-        typeof promise.account !== 'string'
-      ) {
-        // prettier-ignore
-        return Error('Invalid account-add promise missing "account" field: ' + JSON.stringify(promise))
+      switch (promise.type) {
+        case 'follow':
+        case 'account-add':
+          if (typeof promise.account !== 'string') {
+            // prettier-ignore
+            return Error('Invalid promise missing "account" field: ' + JSON.stringify(promise))
+          } else {
+            break
+          }
+        default:
+          // prettier-ignore
+          return Error('Invalid promise type: ' + JSON.stringify(promise))
       }
       return null
     }
@@ -138,22 +150,28 @@ module.exports = {
       const token = bs58.encode(crypto.randomBytes(32))
       promises.set(token, promise)
       save((err, _) => {
-        if (err) return cb(err)
+        // prettier-ignore
+        if (err) return cb(new Error('Failed to save promise file when creating new promise', { cause: err }))
         cb(null, token)
       })
     }
 
     /**
      * @param {string} token
-     * @param {string} id
+     * @param {string} accountID
      * @param {CB<boolean>} cb
      */
-    function follow(token, id, cb) {
+    function follow(token, accountID, cb) {
       if (!loaded) {
-        setTimeout(() => follow(token, id, cb), 100)
+        setTimeout(() => follow(token, accountID, cb), 100)
+        return
+      }
+      try {
+        assertSetPlugin(peer)
+      } catch (err) {
+        cb(/**@type {Error}*/ (err))
         return
       }
-
       if (!promises.has(token)) {
         cb(new Error('Invalid token'))
         return
@@ -163,10 +181,28 @@ module.exports = {
         cb(new Error('Invalid token'))
         return
       }
-      console.log('ppppp-promise mock follow') // FIXME: implement follow
-      promises.delete(token)
-      save(() => {
-        cb(null, true)
+      const myAccountID = promise.account
+      const theirAccountID = accountID
+
+      peer.set.load(myAccountID, (err) => {
+        // prettier-ignore
+        if (err) return cb(new Error(`Failed to load ppppp-set with account "${myAccountID}" when executing follow promise`, { cause: err }))
+        if (peer.set.has('follow', theirAccountID)) {
+          promises.delete(token)
+          cb(null, false)
+          return
+        } else {
+          peer.set.add('follow', theirAccountID, (err, _) => {
+            // prettier-ignore
+            if (err) return cb(new Error(`Failed to follow account "${theirAccountID}" in ppppp-set from account "${myAccountID}" when executing follow promise`, { cause: err }))
+            promises.delete(token)
+            save((err, _) => {
+              // prettier-ignore
+              if (err) return cb(new Error('Failed to save promise file when executing follow promise', { cause: err }))
+              cb(null, true)
+            })
+          })
+        }
       })
     }
 
diff --git a/package.json b/package.json
index 2f43c22..6d557fb 100644
--- a/package.json
+++ b/package.json
@@ -35,6 +35,7 @@
     "ppppp-caps": "github:staltz/ppppp-caps",
     "ppppp-db": "github:staltz/ppppp-db",
     "ppppp-keypair": "github:staltz/ppppp-keypair",
+    "ppppp-set": "github:staltz/ppppp-set",
     "prettier": "^2.6.2",
     "pretty-quick": "^3.1.3",
     "rimraf": "^5.0.1",
diff --git a/test/index.test.js b/test/index.test.js
index 45e459b..13f96eb 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -19,6 +19,7 @@ async function setup() {
     .use(require('secret-stack/plugins/net'))
     .use(require('secret-handshake-ext/secret-stack'))
     .use(require('ppppp-db'))
+    .use(require('ppppp-set'))
     .use(require('../lib'))
     .call(null, {
       shse: { caps },
@@ -36,7 +37,11 @@ async function setup() {
 test('create()', async (t) => {
   const { local, path } = await setup()
 
-  const promise = { type: 'follow' }
+  const account = await p(local.db.account.findOrCreate)({
+    subdomain: 'account',
+  })
+
+  const promise = { type: 'follow', account }
   const token = await p(local.promise.create)(promise)
   assert.strictEqual(typeof token, 'string')
   assert.ok(token.length > 42)
@@ -54,16 +59,25 @@ test('follow()', async (t) => {
 
   assert.rejects(() => p(local.promise.follow)('randomnottoken', 'FRIEND_ID'))
 
-  const promise = { type: 'follow' }
+  const account = await p(local.db.account.findOrCreate)({
+    subdomain: 'account',
+  })
+  await p(local.set.load)(account)
+
+  const promise = { type: 'follow', account }
   const token = await p(local.promise.create)(promise)
 
   const file = Path.join(path, 'promises.json')
   const contentsBefore = fs.readFileSync(file, 'utf-8')
   assert.strictEqual(contentsBefore, JSON.stringify([[token, promise]]))
 
+  assert.equal(local.set.has('follow', 'FRIEND_ID'), false, 'not following')
+
   const result1 = await p(local.promise.follow)(token, 'FRIEND_ID')
   assert.strictEqual(result1, true)
 
+  assert.equal(local.set.has('follow', 'FRIEND_ID'), true, 'following')
+
   const contentsAfter = fs.readFileSync(file, 'utf-8')
   assert.strictEqual(contentsAfter, '[]')
 
@@ -132,7 +146,11 @@ test('accountAdd()', async (t) => {
 test('revoke()', async (t) => {
   const { local, path } = await setup()
 
-  const promise = { type: 'follow' }
+  const account = await p(local.db.account.findOrCreate)({
+    subdomain: 'account',
+  })
+
+  const promise = { type: 'follow', account }
   const token = await p(local.promise.create)(promise)
 
   const file = Path.join(path, 'promises.json')
diff --git a/tsconfig.json b/tsconfig.json
index f6eb639..156adc5 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -6,10 +6,10 @@
     "noEmit": true,
     "exactOptionalPropertyTypes": true,
     "forceConsistentCasingInFileNames": true,
-    "lib": ["es2021", "dom"],
+    "lib": ["es2022", "dom"],
     "module": "node16",
     "skipLibCheck": true,
     "strict": true,
-    "target": "es2021"
+    "target": "es2022"
   }
 }
\ No newline at end of file