The indirect finesse in ♥ has only a 50% chance of success.
The indirect double finesse in ♦ on the other hand will succeed 76% of the time in winning 2 out of 3 tricks.

Declarer therefore must take the double finesse in ♦.
He wins the 1st trick in Dummy with the Q♠, then plays two more rounds of ♠ (removing all Opponents' trumps) ending up in his own hand for trick 4.