After three passes South opened Two no-trumps and, hoping to clinch the rubber, North raised to game. West led the ten of spades against Three no-trumps and, after winning, declarer started on the diamonds. East won and returned a spade, and did so again when he won the next diamond.
Next came the two diamond winners on which East discarded a heart and West a heart and a club. It was not clear to South who held the 13 spade and it seemed an even money chance as to who held the queen of hearts - both defenders had let one heart go. In practice declarer, who had won the last diamond on the table, led a low heart and finessed the jack. West won and cashed the long spade and the defenders still had the ace of clubs to come to defeat the contract.
Even without a sight of the full deal, would you have done better than South? The critical point that he had overlooked was that, to make his contract, he had to find East with the ace of clubs.
Now, if East held this card, together with the two top diamonds that he had already been proved to hold, he could hardly have the queen of hearts as well or he would surely have opened the bidding. Hence, to have any chance at all, declarer must place the ace of clubs with East and the queen of hearts with West.