This conundrum was written by Eddie Kantar and was originally published in the book Kantar for the Defense - Volume 1 - you can find out all about it further down the page.
We are East.
Opening Lead: ♦Q
Which diamond do you play at trick one?
You play the ♦A and declarer ♦9. What do you return at trick two, why?
Any low heart. Before making your play to trick two, you should give some thought to declarer's hand. Remember, he does have a strong two spade opening.
Surely he has the ♦K, the ♥A, solid spades and the ♣K. So what chance do you have knowing, as you do, that the heart finesse works? Well, you know the heart finesse works, but the declarer doesn't. If declarer has the hand you see, his best chance for the contract is to test the clubs by playing the A K and if the queen does not drop, take the heart finesse. What if you play a heart at once?
Declarer will not have time to test the clubs and won't know which play to take. You have put declarer to the test early. Bravo. If declarer rises with the ace of hearts (he probably will), he can no longer make the hand. If you woodenly return a diamond, declarer makes the hand easily by drawing trumps, testing clubs, and later taking the ♥ finesse.
Key Lesson Pointers
1. Try to visualize declarer's hand from the bidding.
2. If you can see that declarer has a choice of plays for his contract, which includes testing a long suit before relying upon a finesse, remove the option by leading the finesse suit before the long suit has been tested.
Kantar invites his reader to direct every play towards the goal of beating the contract in a variety of hands, bringing focus on counting tricks, points and distribution. Problems range from an intermediate to semi-advanced level and knowledge of basic card combinations is assumed. Each book concludes with a complete list of themes for its 100 problems.
It's a conundrum alright. In fact, it's utterly incomprehensible.