Template.viewSingleInvitation.created = function () {
  // Get reference to template instance
  var instance = this;

  // Get File IDs from template instance
  instance.fileIds = instance.data.fileIds;

  // Subscribe to files for this invitation
  instance.subscribe('invitationFiles', instance.fileIds);
};

Template.viewSingleInvitation.helpers({
  'files': function () {
    return Files.find().fetch();
  }
});

@@ -124,82 +124,91 @@
 Get 
-File IDs from template instance%0A  instance.file
+the current invitation ID%0A  var invitation
 Id
-s
  = 
-instance.data.file
+Router.current().params.invitation
 Id
-s
 ;%0A%0A 
@@ -286,32 +286,32 @@
 tion
-Files', instance.file
+Composite', invitation
 Id
-s
 );%0A%7D

Add template-level, composite subscription