South’s 1NT shows 15-17 points and North suggests a slam with 4NT. South could pass on a minimum but here he raises to 6NT.
West leads the jack of spades, won with dummy’s queen and East surprises you by throwing a diamond.
How will you continue?
Seeking further information, you play three top clubs. When West follows all the way, you know that he has only three cards in the red suits.
A 3-3 heart break is therefore very unlikely. A much better prospect is that East holds both the red-suit guards and can be squeezed.
Your next step is to duck a round of hearts. Suppose another heart is returned to dummy’s king. You cross to the ace of diamonds and when West follows, you know that hearts cannot be 3-3.
You continue with the A-K of spades and then play the queen of clubs, throwing a diamond from dummy. East has to find one more discard from Q-9 of hearts and Q-J of diamonds. If he throws a diamond, you will play the diamond king and cross to dummy’s ace of hearts to score the ten of diamonds. If instead East throws a heart, you will play dummy’s ace of hearts and return to the diamond king to score the eight of hearts.
The technique is a criss-cross squeeze.