West   North   East   South
                                 1♠
pass     2♠       pass    4♠
all pass

The ♦4 (fourth best leads) is led against 4♠. Plan the play.

Solution:
Holding both the ♦K and the ♦Q, West would have led the ♦K, so East has at least one diamond honor. There are endplay prospects - one possibility is to eliminate the red suits, and play ♣A and a club, hoping one opponent has the doubleton KQ or fails to unblock with king doubleton. However, the odds of this scenario are not very high. Furthermore, when you lose the lead in one red suit in your attempt to eliminate it, the opponents will lead clubs, and when you lose the lead in the other red suit, they will cash a club, killing the endplay.

The best plan is to play a low diamond at trick one! Consider East's dilemma holding K9xx or Q9xx in diamonds. If he plays the nine, you will score an unexpected trick if you hold 10x of diamonds. Even if East has K10xx in diamonds, he will be scared to play the ten, as you may have Qx of diamonds. East therefore will play the ♦K in practice and switch to the ♥K. Now it is only a matter of drawing trumps (ending in hand), playing a diamond to the jack, and discarding your heart loser on the ♦A.

Analysis:
A double dummy analysis is not appropriate for this deal.
Par Contract Analysis:
The par contract on this deal is 3♠ by North-South.

Bridge Baron deal No : N3640-17523-00966-18360-89178-57387