After three passes, South opened One Heart. North raised to Three Hearts and it was easy for South to go on to game.
West led the ace of clubs against Four Hearts and, after cashing the king as well, switched to the jack of diamonds. Still unworried at this point, declarer won with dummy's queen and took a losing trump finesse. West won with his king and exited with a trump.
Now, as South had already lost three tricks, everything depended on how he played the spades. If you think of the suit in isolation, then he played with the odds when he cashed the king and followed with a finesse of the jack, only to lose to East's queen and so go one down.
What was the vital clue that declarer missed? It was that West had dealt and passed! In the play so far he had shown up with the ace and king of clubs, the king of hearts and the jack of diamonds. Even the most conservative of players would have opened the bidding if he had held the queen of spades as well! The only chance, therefore, was to find East with the doubleton queen of spades.Reuse content