You are South, holding this hand, playing Duplicate Pairs.
Your opponents are vulnerable; your side is not.
N E S W
NB 2C 4S 5C
East's 2C Opening Bid was a Game-force, and the strongest bid available to his side.
South led Ks, and East drew trumps and ran four club tricks to make his Grand Slam. What could South have done to improve the situation and his side's score?
These weird, distributional hands are always difficult to judge, but I always like to ask myself two questions:
How do I think the bidding will progress?
Is there any way to obtain crucial information from partner?
To answer the first question is difficult. Partner has passed and our hand appears to contain no defence whatsoever. Since we have a 9-card suit, the chances are that East's 2C opening bid indicates a distributional hand also, probably containing a 7-card suit or longer. I am fairly confident that E/W can make 11 tricks and, depending upon how many aces my partner holds, perhaps 12 or 13. It is possible that my singleton in both minor suits, heralds a bad trump break from East, but I am not relying on it.
Finally, if the opponents bid, say 5C or 5D, will I be content to leave them there? I probably won't but, if I bid 4S, I have made my pre-emptive bid and, once I have pre-empted, I must not bid again. Maybe they will make 13 tricks in 5C or 5D - I certainly don't want to push them into a slam they haven't bid.
So, is 4S the best bid available?
I think there is a better bid and it helps me to answer the second question: can I get important information from partner?
I am going to bid 4NT!
Yes, this is Blackwood (even if you are playing RKCB, I think this must simply be ordinary Blackwood). Assuming that West passes, partner will show me how many aces he holds. If it is none, then E/W might be able to make a Grand Slam; if it is one; then a small slam seems likely, and if North holds two, then the five level will likely be high enough. Now, I can judge when to bid 5S, 6S or 7S.
If West bids - which, here, I think he should, now does your partnership know DOPI? (a simple way to bid after intervention over a 4NT enquiry). Look it up in "The Right Way To Play Bridge" if not.
Here's the full deal:
As it is, when I know partner has no aces, and I assume that West's 5C bid over my 4NT bid shows a high quality suit, when East bids 7H, I can bid 7S. And, yes, I know that East can bid 7NT, but that's easy seeing all the cards and much harder when you can't. 7S doubled is five down doubled for -1100, opposed to scoring - 2210 for East making 7H.