This deal was played in the South Florida Bridge Players Imp Game, reported to me by David Berkowitz. With both sides vulnerable, the opponents reach 3NT as shown. Partner leads a standard 3, dummy plays low, you play the king and declarer plays the 5. Now what?

Vul:Both Dlr: North	92  A  AKQJ982  654
Partner		K1064  J983  1054  AQ
	Declarer

West	North	East	South
	1	Pass	1
Pass	3	Pass	3NT
Pass	Pass	Pass

You can see that declarer has 8 tricks in dummy, but is there a 9th?

Did you woodenly return partner's suit? If so, the 4 (low from three) is the correct play. Did you try the A at trick two to look for a signal? Something ese? This was the Real Deal:

Vul:Both Dlr: North	92  A  AKQJ982  654
A873  K107  763  872		K1064  J983  1054  AQ
	QJ5  Q6542  --  KJ1093

If you play the A, declarer will have a lot of tricks.  There is no good reason to make that play. Nor is there a need to return a spade. You should play a heart at trick two. Why?

Because you have the 10xx, you know declarer can't get to his hand right away. Even if he has the K, he has no quick entry. If he tries to get to his hand with the K, you win the A and play spades. If they run, you'll set it. If they don't run, returning a spade at trick two wouldn't have done any better.

If you return a low spade, partner wins and maybe figures out the killing defense (a low heart return). 

Why rely on partner? Play the 3 at trick 2.

Your heart play gives declarer only his sure 8 tricks--not enough.

When declarer runs diamonds, partner will signal you. He will discourage in clubs and throw some spades. That way, when declarer eventually plays a club, you will know to win your ace and play a second round of hearts for down one.