North leads the Club 5.  Declarer calls for a low Club, but Dummy places the Ace in the played position.  South plays the Club 7.  Declarer wins the Club Q.

At this point Dummy asks, "Did you mean to play the Ace?"  Decalrer responds "No, I called for a low Club."  At this point the defenders call for the Director.  How should director rule?  Ace is retracted, Queen wins the trick, and play on.  Ace and Queen are both played at trick 1.  Something else?