Discard and lead the right cards

John Buchan, a Scottish politician and novelist, whose most famous book was The Thirty-Nine Steps said, Every man at the bottom of his heart believes that he is a born detective."

It helps if a bridge player is a detective, uncovering clues from the bidding and play. But another word in that sentence is important in today's deal.

South is in three no-trump. West leads the spade queen. Given that the defenders can take only four tricks in spades, how should declarer plan to win the last nine?

South starts with six top tricks: four hearts, one diamond and one club. He needs to deduce that if the club finesse is losing, the contract is hopeless. But if that finesse is winning, he can rake in nine tricks: four hearts, one diamond and four clubs. So, on the fourth spade, declarer must discard his diamond queen. Yes, this risks going several down if the club finesse fails, but pitching a club instead would leave South needing both minor-suit finesses to work.

Then, after taking the fifth trick with his diamond ace, how should declarer continue?

He must realize that he might need to take the club finesse three times. But he has only one dummy entry, in hearts, and he must stay in the dummy while repeating the club finesse.

This requires first leading the bottom card in dummy's clubs that can hold the trick when East has the club king. South must lead first the club nine. When that holds, he runs the club jack. Then he plays a club to his queen and claims.

If declarer first leads dummy's club jack, East can defeat the contract. Work out how.