This deal is from the Northern Bridge League earlier this month.
The bidding and play did not go like this at the table, but it is an interesting defensive problem.
You choose to lead the heart queen against four spades, declarer plays the ace from dummy, partner plays the king of hearts and declarer the six.
Plan your defence.
Declarer will play a spade to hand and then a diamond, you must play the king to prevent him making two diamond tricks.
If you play second hand low he will finesse the eight, losing to the queen and subsequently finesse the jack and get a discard on the ace of diamonds.
The full deal was
Note that only a heart lead beats the contract, on a club lead for example declarer can play on diamonds and get two tricks in the suit even if you play the king on the first trick as there is still a heart entry in dummy.