This deal was well-defended against me in a knockout team event at a recent local Regional (a rare playing-appearance by me). West held:

Q54
KQJ9
2
AQ983.

At favorable vulnerability, his partner opened 2. RHO (me) passed, and he raised to 4. LHO (David Berkowitz) doubled, and I took it out to 5 which bought the contract. The K produced this dummy:

Vul:N-S Dlr: East	A A10762 AJ105 1054
Q54 KQJ9 2 AQ983

The K drew the 2, 4 and 8 (standard signals). Now what?

If declarer has three hearts, the contract will surely be defeated (West has 2 heart tricks and at least 1 club).

More likely is that both declarer and partner have two hearts.

If so, the correct play at trick 2 is the A. Why?

If declarer has the K there is no way to set it (unless partner has an unlikely trump trick -- in which case the A will set it anyway).

Why can't West hope for 2 club tricks when declarer has the K? That would mean declarer started with 3=2=5=3 shape. He'd be able to set up one heart discard and have to lose 2 club tricks. But, declarer won't have that shape. With a flat hand such as that, he would pass the double of 4. It would be wrong to take out a double to the five level with a flat hand. Declarer assumed that I'd have at least a sixth diamond for my 5 bid which meant 3=2=6=2. In that case, without a club switch, I'd be able to set up the hearts to throw a club and make the contract. After long consideration, West correctly found the club switch at trick two. This was the real deal:

Vul:N-S Dlr: East	A A10762 AJ105 1054
Q54 KQJ9 2 AQ983		KJ10983 54 74 K76
	762 83 KQ9863 J2

As you can see, my opponent was right. I had ducked rather smoothly at trick one (my only chance), hoping for a lazy heart continuation. In that case, I'd have been able to set up the hearts and make my contract for +600. I congratulated my opponent (I should have gotten his name) on his thoughtful defense for down one.

It turns out, this defense didn't gain West as much as you'd think. At the other table, after the same start, North passed. My teammates made an easy 420 in 4 and we won 8 IMPs. Had West misdefended at my table, we would have won 14 IMPs.