Overcoming Obstacles

Dlr: South ♠ A Q 7 5
Vul: E-W K 5
A 6 5 2
♣ K Q J
♠ 4
A Q J 6 4 3
8 4 3
♣ A 7 5
West North East South
1
1♠ Dbl Pass 2
Pass 4NT (1) Pass 5♠ (2)
Pass 6 All Pass

(1) Roman Key Card Blackwood
(2) Two key cards and the trump queen
West leads the K against your slam. Do you see any dangers ahead?

Solution

Declarer saw that if trumps were no worse than 4-1, he would make six trumps, four tricks in the minors and presumably two spades. Nothing would save the contract if West had five trumps, so his problem became, “What could be done if East had five trumps?”
Declarer deduced that the answer was to elope with his trumps by ruffing dummy’s low spades in hand. If trumps were 5-0, he saw that any successful play would involve cashing three clubs before taking a spade ruff.
With that in mind, after winning the first trick with the dummy’s A, declarer made the strange-looking play of a low trump from dummy to his jack. When West discarded a spade, declarer’s precautions regarding a possible foul trump division had paid off. He finessed the ♠Q and cashed the ♠A, throwing a diamond from hand.
Now came the point of the play in trumps: Instead of leading a spade at this point, declarer cashed his club winners, ending in dummy. Only then did he call for dummy’s ♠5. If East had ruffed high, declarer would have thrown a diamond: He would then have had the rest of the tricks. When East discarded a diamond, declarer ruffed low and led a trump to dummy’s king. When declarer played a fourth spade from dummy, East ruffed with the 10 and declarer threw his remaining diamond. Declarer then claimed his contract, making two spades, six trumps, a diamond and three clubs.
Note that if the K had been played on the first round of the suit, the contract would have failed because East would have discarded a club on the third round of spades and declarer would then have had no way home, lacking the required entries to dummy. The full deal:

Dlr: South ♠ A Q 7 5
Vul: E-W K 5
A 6 5 2
♣ K Q J
♠ K J 9 8 3 2 ♠ 10 6
10 9 8 7 2
K Q J 10 9 7
♣ 9 6 4 2 ♣ 10 8 3
♠ 4
A Q J 6 4 3
8 4 3
♣ A 7 5