The 3NT game looks simple enough: three hearts (four with a heart opening lead), three clubs, four spades (with the Q-10 dropping doubleton) and probably  a diamond trick.

West led a heart, won by dummy’s 10, and declarer called for the ♣K. West took her ace and led another heart to the king.

Declarer cashed her three club tricks, finishing in her hand. On the last club, Merblum (East) discarded a low diamond.

To declarer, this seemed a chance to set up a diamond trick. She led the ♦J and passed it – and Merblum ducked! Certain the ♦Q was favorably placed,  declarer next finessed the ♦10 and watched as Merblum won the queen, the ace and two more diamonds to set the contract.