This deal is from the Corwen Trophy, the EBU inter-county pairs held last month at Daventry.
After a simple auction John Holland received a small heart lead against three notrump. East won the ace and returned the four to John's king. John now immediately played a spade, West naturally ducked and the queen won in dummy. John now played a club to the king, took the club finesse and cashed the ace of clubs to find that the clubs weren't breaking. He now turned his attention to the diamonds, when those broke he emerged with twelve tricks and most of the match points.
John had reasoned that one (but not both) of the minor suits was likely to provide five tricks and if he could slip a spade through he might be able to get twelve tricks. If East had held the spade ace, he would probably win the spade and continue hearts, so there was nothing to lose by playing a spade at trick three.