This contract seems to depend on holding your trump losers to one and relying on West to have the ♦Q. If that was the only way to make 4♥, you wouldn’t be reading about this problem here. Suppose the full deal is something like this:
After taking the first trick with dummy’s ♠K, cross to hand with the ♠A and lead a club.
West will surely play low and dummy’s queen will be taken by East with his king. East cannot attack diamonds without losing a trick, so he shifts to a trump. You take this with the ace, ruff your spade, eliminating the suit, and lead a second club.
When West takes this and shifts to a diamond, you counter by winning it with the ace then playing a trump to endplay East. The return of a black suit concedes a ruff-and-discard while the alternative is into to lead a diamond into dummy’s K-J tenace. So, despite the ♦Q being wrong, the game can sometimes be made!
