South opened One Spade, West doubled, East responded Two Dia- monds, South fought on with Two Spades and, after two passes, East doubled to end the auction. West led his singleton trump against Two Spades doubled and, after winning in dummy, declarer led dummy's jack of diamonds. East played low and South's king was covered by an ace. West continued with the ace of clubs but South was able to point out that it was not his lead. West had "won" the previous trick with the wrong red ace!
What was the effect of West's move? The revoke was established (for he had led to the next trick) so it was South's king of diamonds that had won the trick. The ace of hearts had gone, so declarer had no heart losers, and the ace of clubs was an exposed card that had to be played at the first legal opportunity.
South now led the ace of trumps and West was forced to discard his ace of clubs. East then came to his three trump tricks but, under the laws applying at that time, the penalty for West's revoke was two tricks. So declarer ended with no fewer than four doubled overtricks. It must be rare to lose three aces in the space of one trick!