Bridge - The Scotsman 28/11/2012
There are various ways of using the redouble here; perhaps the most popular is the Helvic convention where the redouble is used to show a single-suited hand. Over the redouble opener bids 2C in case that is partner’s suit. If no-one doubles that responder may pass; if 2C is doubled he reveals his real suit, as here when South bids 2D. West decides to double because all his values are in diamonds, and there is nowhere further to run.
The redouble has fulfilled its purpose. West cannot gain the lead to draw a third round of trump, so declarer negotiates a club ruff in dummy to go with four trump tricks in his own hand, the ace of clubs and a slow trick in one major or the other. One down is a clear improvement over 1NT doubled: East leads a club and West holds up his ace of diamond till the third round. Declarer may abandon diamonds after two rounds, but whatever he does four more rounds of clubs weaken the North hand and he must go at least two down.