Start today by looking at the South hand. North opens one heart, South responds one spade, and North rebids two diamonds. What should South do now?
I do not mind North's thin opening bid. He had an easy rebid and was nonvulnerable. South had two choices. He could have rebid three no-trump, which risked ending the auction when game or slam in diamonds would have been better. But to bid three clubs, fourth-suit game-forcing, was not without risk either. At the table, South went for the most likely game: three no-trump. (Note that five diamonds was hopeless.)
What should declarer have done after West surprisingly led a low diamond?
South had only three top tricks: one spade and two diamonds. But obviously he had potential winners in all four suits, the most profitable being hearts. What was the percentage play for four heart tricks?
Declarer took the first trick with his diamond king over East's queen, then ran the heart nine. When it held, he continued with a heart to dummy's eight. East took that trick and shifted to a low club. West won South's king with his ace and returned the club 10, which declarer ducked. South took the third club and led the spade queen: king, ace. Now declarer ran the heart suit, which squeezed West between spades and diamonds, so the contract made with an overtrick.