West opened One Heart and following two passes South bid One Spade. West rebid his hearts, North supported spades and South bid game.
Against Four Spades West led the eight of diamonds. Declarer took this as dummy and led the queen of spades, which lost to West's singleton king. West now played the ace of hearts and, on seeing East's encouraging seven, continued with a low one.
In with the king, East promptly switched to a club and the contract was defeated by two tricks.
So what inference had declarer missed? West had bid hearts twice, yet had not led one. Therefore his suit could not be solid - probably A Q to six - for if the suit had been headed by the A K Q or even K Q he would surely have preferred that attack. Therefore East should hold the king of hearts. He can't have had the king of spades as well, otherwise, with six points, he would have responded to West's opening bid.
Therefore declarer's only real chance was that the king of spades was bare in the West hand, and so he should have laid down the ace. After completing the drawing of trumps he cashes his diamonds, discarding a heart from dummy. Now he loses just one heart and two clubs.
Game all; dealer West
4Q J 9 4
#K Q 9
2J 10 7 4
4K 47 3 2
!A Q 10 9 8 6 !K 7 2
#8 2 #6 5 4 3
2A Q 8 3 29 6 2
4A 10 8 6 5
#A J 10 7