This deal is a variation on a deal presented in the February, 2013 ACBL Bulletin. The original problem was for declarer in 3NT, but I like it as a defensive problem for West. He holds the West cards here:

 

 

Vul: None Dlr: South	AQ107 765 632 763
4 A1082 109854 KJ10		EAST
	SOUTH

South opened 2NT (20-21), raised to 3NT by North. West chose to lead a 4th best diamond (I prefer the 10). East plays the 7 and declarer wins with the A.

 

Next comes the J from declarer. Do you play high or low. If high, what would you play next?   Think this through carefully before reading the answer below.

 

 

 

It seems declarer has KQJ(x).  No other heart holding makes sense. With QJx(x) or KJx(x), he would lead the suit from dummy.  What about his diamond holding? Partner played 3rd hand high and could produce only the 7 at trick one. So, declarer has AKQJ in addition to KQJ.  That's 16 HCP.  Can he also have the AQ? No.

 

Furthermore, it looks as if he might be planning to steal this heart trick and then revert to spades for his 9 tricks. You should win the A immediately and switch to clubs (the proper/standard card would be the J). This is the full deal:

 

 

Vul: None Dlr: South	AQ107 765 632 763
4 A1082 109854 KJ10		K8532 93 7 Q9854
	J96 KQJ4 AKQJ A2

 As you can see, declarer did well not to take the spade finesse immediately. After it lost, East would have an easy club switch. Declarer would have only 3 spade tricks to go with 4 diamonds and 1 clubs.  So, he tried (as the declarer play article suggested) to steal a heart trick first. Had the J won the trick, he then could have taken the spade finesse, but would have 9 tricks when it lost.

 

If the K were onside, declarer would always have 9 tricks.

 

With the K wrong, his attempt to sneak a heart trick would be scuttled if you figured out to win the A and heroically switch to the J. Now, when declarer wins and tests hearts, he is a trick short. He would take the spade finesse and finish down 2.