The full hand for the play problem was:
You were playing a strong no trump, which is why you opened what might have been a prepared club. North leads a low heart.
The contract is only in danger if North has the A and South has the K. Is there anything you can do in this situation?
At trick two I tried the effect of cashing the A and leading a low diamond. Had I lost the trick to the K on my left, I would still have made the contract: even if the A was sitting over the king, South would not have an entry and a spade could be discarded on the queen of diamonds.
The bonus came when South failed to play the king at trick two (thinking that I wouldn't play the diamond suit in this way with anything other than a singleton). When the jack scored, I was home. Had he risen, I would have gone off, but I would have gone off anyway on any other line.
This is the sort of play which will work more often then it ought to, and in case you think the opposition in this instance were weak, I would point out that RHO was one of England's top players, and the partnership was a recent winner of the Corwen trophy.
[Nice line. It would have failed if North had held say AJxx J10xx Kxxxx -, when partner might have argued that the finesse was superior! Apologies to Giles for the title - I dare say he's heard it before (ed.)]