If partner opens one of a suit and you respond in a lower-ranking suit at the two-level, you will usually have a good hand — but not always. What happens if righty throws in a takeout double? How does that affect the meaning of a two-over-one response?
In the United States, this response is traditionally treated as weak and nonforcing. When the responder has 10-plus points, the "normal" requirement for a two-over-one, he starts with redouble.
The North hand is a good example. After one heart — (pass), North would have to respond one no-trump. (Yes, some players would bid three diamonds, a weak-jump response. I do not like that bid, although I understand that it can occasionally work well.) But after one heart — (double), North can bid two diamonds, describing his hand much more accurately. And after East passes, South jumps to three no-trump.
West leads his fourth-highest club. How should South plan the play?
If East had bid two spades over two diamonds, it would have been very aggressive, especially since there was no guarantee of a 4-4 fit.
South has only four top tricks: two hearts and two clubs (given the lead). But he can get five more tricks from the diamond suit. However, if the defender with the diamond ace holds up that card until the second round of the suit, declarer will need a dummy entry. Where is the only entry?
Right — in clubs. South must take the first trick with his club ace, not with the jack on the board. Then he drives out the diamond ace and later forces a dummy entry in clubs.