You receive the 6H lead, Plan the play.
This hand looks pretty easy unless Diamonds are 4-1. If diamonds are 4-1, you need RHO to have the 4 card Diamond suit, so you can lead through him, eventually finessing him out of his trump trick by ending in dummy at trick 11. This is called a trump coup. In order to successfully execute a trump coup, you need to shorten your hand to the same number of trumps as defender with long trumps. In addition to shortening your hand, you need to be in dummy at trick 11, in other words, you need to be able to lead through the defender with long trumps. Sometimes it will take a little foresight to shorten your hand successfully... This may mean making a play before you know about the bad split as a precaution, so that you have sufficient entries later.
Solution: Win the opening lead with the King in hand, play a trump to the queen and ruff a club to begin shortening yourself simply as a precaution, since anything but a 4-1 Diamond split will see the contract home. Now when you play another trump to dummy and receive the bad news, you will have sufficient entries to execute the trump coup. Now ruff another club from dummy, and play the Jack of Hearts, ducking from dummy, leaving this position:
Cash the Ace of spades from your hand, lead a spade to the queen and lead all your top hearts. North cannot ruff, because then he will give up his trump trick, so North must pitch. You also pitch when North pitches. You repeat this 3 times, pitching the rest of your spades from your hand, ending in dummy at Trick 11 to lead a trump through North, whose trump trick magically disappeared!
The full deal:
The key to the hand was a "what can go wrong" mentality. Ruffing a club before playing the 2ND trump from dummy gives you enough entries to shorten yourself and use this fun technique.