[shyams]

Scoring: MP

Bidding:
East - South - West - North
(Pass) - 1H - (4S) - all pass
N/S play 5-card majors

North leads HT at trick 2 (hi-lo=even carding)

1. N: HT-2-Q-4
2. S: HK-7-3-9
3. S: HA-SQ-etc

North & East hands + Declarer's play for the rest of the tricks printed in "hidden" font

Spoiler

Declarer carefully cashes SK, enters dummy (DQ-to-DA),
plays Sx agonises for a while then puts up SA. Making 4S!

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[WesleyC]

My first impression was to switch to a club at Trick 3, but I thought it was pretty much a guess.

I've been messing around with Deal 3.17 lately and decided to use it and sim the situation.

Considering only cases where the choice of return will influence whether the contract goes down:

A Heart return is required if:

North has ♠Qx or ♠Q and declarer must lose exactly 1 trick in clubs/diamonds OR
North has ♠AJ and declarer has no losers in clubs/diamonds.

And a Club return is required if:

Declarer has ♣KQ, ♣KQJ or ♣KQJx and no loser in diamonds.

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In the simulation I made the following assumptions:

1. West has 7+ spades.
2. North has 10 HCP or less.
- based on the fact that he didn't make a negative double.
- note this means West has at least 12 HCP
3. The more balanced West is, the more HCP he needs for his 4S bid.
- 7222, 16+ HCP
- 7321, 14+ HCP
- 7420, 12+ HCP
- Any 8 or 9c suit, 12+ HCP

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I analysed the results over 100,000 deals.

Most of the time the contract was either doomed or making independent of South's decision at trick 3. Of the times where South's decision mattered:

Playing for the trump promotion set the contract 5782 times.
Playing for a club ruff set the contract 4422 times.

At least in terms of setting the contract, it seems South made the right play.

[TylerE]

Wesley, I'm not sure your assumptions are right. First off, are we REALLY expecting north to make a negative X at the *4 level* on any 10 count?? I also think you're being way too conservative in assigning hands to west. At least around here, 4♠ is a lot more likely to be something like, say

♠ AQJxxxx ♥ xx ♦ x ♣ KJx than some stronger hand.

[WesleyC]

If West has the hand you suggest then North holds: Kx xx Qxxxx AQxx which I think is an easy double, especially when the opponents are favourable. I'd feel somewhat justified on this layout because we can make 5D if partner chooses to bid or get 300/500 out of 4Sx if he passes.

I can easily change the setup though, if you give me some different assumptions about what hands north holds to pass.

[shyams]

Thank you, Wesley, for the simulation

I held the South hand. At the table, I thought I blundered by not switching to a low club. But after the event when I was going thru the hand records I felt it was too close to call. That's why the post.

[Trumpace]

Funny. A play problem with no clear consensus. Are the two options really that close?