diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index 457be534e8..189da4ee91 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1483,6 +1483,7 @@ phutil_register_library_map(array(
     'PhabricatorCalendarDAO' => 'applications/calendar/storage/PhabricatorCalendarDAO.php',
     'PhabricatorCalendarEvent' => 'applications/calendar/storage/PhabricatorCalendarEvent.php',
     'PhabricatorCalendarEventCancelController' => 'applications/calendar/controller/PhabricatorCalendarEventCancelController.php',
+    'PhabricatorCalendarEventCommentController' => 'applications/calendar/controller/PhabricatorCalendarEventCommentController.php',
     'PhabricatorCalendarEventEditController' => 'applications/calendar/controller/PhabricatorCalendarEventEditController.php',
     'PhabricatorCalendarEventEditor' => 'applications/calendar/editor/PhabricatorCalendarEventEditor.php',
     'PhabricatorCalendarEventInvalidEpochException' => 'applications/calendar/exception/PhabricatorCalendarEventInvalidEpochException.php',
@@ -4818,6 +4819,7 @@ phutil_register_library_map(array(
       'PhabricatorFlaggableInterface',
     ),
     'PhabricatorCalendarEventCancelController' => 'PhabricatorCalendarController',
+    'PhabricatorCalendarEventCommentController' => 'PhabricatorCalendarController',
     'PhabricatorCalendarEventEditController' => 'PhabricatorCalendarController',
     'PhabricatorCalendarEventEditor' => 'PhabricatorApplicationTransactionEditor',
     'PhabricatorCalendarEventInvalidEpochException' => 'Exception',
diff --git a/src/applications/calendar/application/PhabricatorCalendarApplication.php b/src/applications/calendar/application/PhabricatorCalendarApplication.php
index b0b5d817ff..c77e697ae8 100644
--- a/src/applications/calendar/application/PhabricatorCalendarApplication.php
+++ b/src/applications/calendar/application/PhabricatorCalendarApplication.php
@@ -55,6 +55,8 @@ final class PhabricatorCalendarApplication extends PhabricatorApplication {
             => 'PhabricatorCalendarEventCancelController',
           '(?P<action>join|decline|accept)/(?P<id>[1-9]\d*)/'
             => 'PhabricatorCalendarEventJoinController',
+          'comment/(?P<id>[1-9]\d*)/'
+            => 'PhabricatorCalendarEventCommentController',
         ),
       ),
     );
diff --git a/src/applications/calendar/controller/PhabricatorCalendarEventCommentController.php b/src/applications/calendar/controller/PhabricatorCalendarEventCommentController.php
new file mode 100644
index 0000000000..4d31b020c4
--- /dev/null
+++ b/src/applications/calendar/controller/PhabricatorCalendarEventCommentController.php
@@ -0,0 +1,69 @@
+<?php
+
+final class PhabricatorCalendarEventCommentController
+  extends PhabricatorCalendarController {
+
+  private $id;
+
+
+  public function willProcessRequest(array $data) {
+    $this->id = idx($data, 'id');
+  }
+
+  public function handleRequest(AphrontRequest $request) {
+    $user = $request->getUser();
+
+    if (!$request->isFormPost()) {
+      return new Aphront400Response();
+    }
+
+    $event = id(new PhabricatorCalendarEventQuery())
+      ->setViewer($user)
+      ->withIDs(array($this->id))
+      ->executeOne();
+    if (!$event) {
+      return new Aphront404Response();
+    }
+
+    $is_preview = $request->isPreviewRequest();
+    $draft = PhabricatorDraft::buildFromRequest($request);
+
+    $view_uri = '/'.$event->getMonogram();
+
+    $xactions = array();
+    $xactions[] = id(new PhabricatorCalendarEventTransaction())
+      ->setTransactionType(PhabricatorTransactions::TYPE_COMMENT)
+      ->attachComment(
+        id(new PhabricatorCalendarEventTransactionComment())
+          ->setContent($request->getStr('comment')));
+
+    $editor = id(new PhabricatorCalendarEventEditor())
+      ->setActor($user)
+      ->setContinueOnNoEffect($request->isContinueRequest())
+      ->setContentSourceFromRequest($request)
+      ->setIsPreview($is_preview);
+
+    try {
+      $xactions = $editor->applyTransactions($event, $xactions);
+    } catch (PhabricatorApplicationTransactionNoEffectException $ex) {
+      return id(new PhabricatorApplicationTransactionNoEffectResponse())
+        ->setCancelURI($view_uri)
+        ->setException($ex);
+    }
+
+    if ($draft) {
+      $draft->replaceOrDelete();
+    }
+
+    if ($request->isAjax() && $is_preview) {
+      return id(new PhabricatorApplicationTransactionResponse())
+        ->setViewer($user)
+        ->setTransactions($xactions)
+        ->setIsPreview($is_preview);
+    } else {
+      return id(new AphrontRedirectResponse())
+        ->setURI($view_uri);
+    }
+  }
+
+}
diff --git a/src/applications/calendar/controller/PhabricatorCalendarEventViewController.php b/src/applications/calendar/controller/PhabricatorCalendarEventViewController.php
index 0019ad0717..32ca36f306 100644
--- a/src/applications/calendar/controller/PhabricatorCalendarEventViewController.php
+++ b/src/applications/calendar/controller/PhabricatorCalendarEventViewController.php
@@ -43,11 +43,26 @@ final class PhabricatorCalendarEventViewController
       ->setHeader($header)
       ->addPropertyList($properties);
 
+    $is_serious = PhabricatorEnv::getEnvConfig('phabricator.serious-business');
+    $add_comment_header = $is_serious
+      ? pht('Add Comment')
+      : pht('Add To Plate');
+    $draft = PhabricatorDraft::newFromUserAndKey($viewer, $event->getPHID());
+    $add_comment_form = id(new PhabricatorApplicationTransactionCommentView())
+      ->setUser($viewer)
+      ->setObjectPHID($event->getPHID())
+      ->setDraft($draft)
+      ->setHeaderText($add_comment_header)
+      ->setAction(
+        $this->getApplicationURI('/event/comment/'.$event->getID().'/'))
+      ->setSubmitButtonName(pht('Add Comment'));
+
     return $this->buildApplicationPage(
       array(
         $crumbs,
         $box,
         $timeline,
+        $add_comment_form,
       ),
       array(
         'title' => $page_title,
diff --git a/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php b/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
index ea8b006ffd..340facf36c 100644
--- a/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
+++ b/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
@@ -22,6 +22,7 @@ final class PhabricatorCalendarEventEditor
     $types[] = PhabricatorCalendarEventTransaction::TYPE_CANCEL;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_INVITE;
 
+    $types[] = PhabricatorTransactions::TYPE_COMMENT;
     $types[] = PhabricatorTransactions::TYPE_VIEW_POLICY;
     $types[] = PhabricatorTransactions::TYPE_EDIT_POLICY;
 
@@ -119,6 +120,7 @@ final class PhabricatorCalendarEventEditor
         $object->setIsCancelled((int)$xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
+      case PhabricatorTransactions::TYPE_COMMENT:
       case PhabricatorTransactions::TYPE_VIEW_POLICY:
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
       case PhabricatorTransactions::TYPE_EDGE:
@@ -167,6 +169,7 @@ final class PhabricatorCalendarEventEditor
             ->save();
         }
         return;
+      case PhabricatorTransactions::TYPE_COMMENT:
       case PhabricatorTransactions::TYPE_VIEW_POLICY:
       case PhabricatorTransactions::TYPE_EDIT_POLICY:
       case PhabricatorTransactions::TYPE_EDGE: