Get partner in

Now that BBO runs free daily MP tournaments, I try to catch them when I can.  Time constraints man that I've pretty much stopped playing the bridgez/wbridge5 one.

Here's a hand from yesterday's:

I started off with the Queen of spades lead and declarer (East) immediately led a heart. I ducked and the robot guessed right to go up with the King of hearts.

Next, three low clubs to my singleton King.  Nice playing by the robot ... I continued spades and after the robot ruffed in hand, the four of hearts was led.

What should I play?

I desperately need to get partner in to lead diamonds through. I need to duck this trick.  If declarer has the queen of hearts, I can't lose my Ace-of-hearts trick, but if partner has it, then he can lead a diamond through.

Beating 3C by two tricks (instead of one) was the difference between 68% and 38%.