Against your normal 6NT contract, West leads the ♥10. How do you plan to get to 12 tricks?
With 11 top tricks and 12 if spades were 4-1, declarer looked at the possibility of a spade-diamond squeeze against the defender with long spades if they were 5-0. Declarer saw that, if he cashed even one spade and ducked a diamond, a defender with five spades could win it and return a spade, killing the squeeze.
In order to cater for to eventualities, declarer won the first trick with the ♥A, then cashed the ♥K and the top two clubs. Then he led a low spade to dummy’s queen. West’s discard turned a potential 12 tricks into 11. While taken aback by this development, declarer had prepared well. He continued with a low diamond from the table and, when East played the jack, declarer took this with the king, then ran the ♦10 to East’s queen. East exited with the ♠J. Declarer took this in dummy with the ace. He cashed the ♦A and jettisoned the ♥Q from hand. Declarer continued with the ♥J and repeated the maneuver by discarding the ♣Q from hand, thereby bringing everyone down to three cards. East was reduced to the ♠10 9 and the ♦9. When the ♣ was played, East had no winning discard. If he had followed to the first diamond with a low one, declarer planned to cover it with the 10. That would prove to be a winning play when East had begun with three diamonds, including the 9 and at least one honor. Otherwise, the same squeeze would have operated.
The full deal: