That’s a good plan, but the devil is in the details.  For that line to work, Declarer will be sure to use high trumps for any Diamond ruffs.  And Declarer must also pay careful attention to the Heart spots.  If, for example, on the first round of trumps, he plays the Heart Six to Dummy’s Jack then he can kiss the contract goodbye.  It has to be the Six to the Seven, and so on.

With those caveats in mind, the play is simple enough.  After winning the ♠A, Declarer cashes the ♦A, crosses to Dummy with a trump (say the Six to the Seven), runs the ♦J around to West’s Queen (pitching a Spade), ruffs the Spade return high, and gets to Dummy with another trump.  Another Diamond is led, East plays the King and Declarer ruffs (high, of course).  Now it’s over to Dummy with yet another trump, and the established Diamonds are enjoyed.  The full deal:

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