I played this deal in my newest source for material--an online money game. With both sides vulnerable, IMP scoring, I held:

 J65  
 Q1052  
 AQ6  
 A97

I dealt and opened 1 and partner responded 1. I rebid 1NT, of course, and he raised to 3NT. LHO led the 6 and I saw:

KQ103 4 K42 K10863

J65 Q1052 AQ6 A97

Partner has taken the high road with his 11 HCP (potentially facing only 12 HCP). I suppose he loved the club fit and source of tricks. He has put his faith in you.

You have only 5 top tricks (3 diamonds and 2 clubs). RHO wins the K and returns the J. That gives you a heart trick to get up to 6 tricks. What is the plan? If you play the queen, LHO wins the ace and plays another heart. Should you work on clubs or spades?

Those who know me will recognize the trick question. If you cover the J, you are on your way to down 1. Why shouldn't you cover?

First of all, can we agree that working on clubs is the wrong plan. Barring a miracle in clubs, you will have to give up a club trick. The defense will have a club, the A and at least 3 heart tricks (even if they are 4-4). So, you will have to work on spades.

Once you knock out the A, you will have 3 spades to go with 3 diamonds, 2 clubs and the heart trick. The danger is that the defense takes 4 heart tricks and the A.

If hearts are 4-4, you will have no trouble. If opening leader has 5 hearts and the A, you have no chance. What if hearts are 5-3 and RHO has the A? When you cover the J, LHO will duck! When RHO gets in with the A, he will play another heart through you. Can you prevent this? Yes! Don't cover with your Q at trick 2. Now what? East plays another heart (for all he knows, his partner started with A10xxx) and West wins. Look at the full deal:

Vul:Both Dlr: South	KQ103  4  K42  K10863
7  A9763  10875  J54		A9842  KJ8  J93  Q2
	J65  Q1052  AQ6  A97

As you can see, covering the heart leads to defeat. West can duck and then what? East gets in with the A to play his final heart through you. You lose 4 hearts and a spade for down one. If you don't cover the J you are home free. The defense gets only 3 hearts and a spade. You have justified your partner's optimistic jump to 3NT.