Playing five-card majors, South opened One Spade and North responded Three No-Trumps, a "pudding" raise to the spade game, with three-card trump support. South might have decided to pass, but in the event chose to convert to Four Spades.
West led the diamond queen, won by South with the king. Declarer immediately set about trumps, and ran the spade queen to East's king. This was the moment of truth, giving East a chance to shine, but East woodenly returned the heart queen.
South won, drew the outstanding trumps, then led a diamond. West played the 10, dummy the ace, and a third diamond established dummy's nine, for a later club discard from hand, the club honours in dummy providing the entry.
Logically, on the bidding, South must have both top heart honours, as so far he has only shown up with six points for his opening bid. But there is room for West to hold the club 10, and this is the card that East should have played him for. (And, even if South has the 10, he just might omit to insert it!) A low club return drives out one of dummy's honours, and when West gets in with a diamond, a club through dummy's remaining honour sets the contract.