West dutifully lead the club 9. Partner won the AK of clubs and returned the club 8. Declarer pitched a diamond and West ruffed. The high club must show that partner has the spade King, so there are two possibilities for the setting trick, we can either try cashing the diamond ace or leading through dummy's spades, but which shall it be?
If East has the spade king, there's nothing left for declarer but a bunch of hearts to the AK. If he only has seven hearts you can lead your library card, your voter registration card, or anything else that's lying around and he'll still go down. Eight hearts, however, is dangerous, here are two possible holdings for South:
With South #1 a spade lead will beat it and ace of diamonds will allow him to make (remember, the heart Jack is an entry). With South #2 the ace of diamonds will beat it and a spade will allow him to make. So what's your lead?