Redouble Manqué

A Q 8 2
A 8 7 6
5
K J 9 2
10 4 7
K 10 4 3 2 9 5
A 7 2 K J 10 6
A 7 4 Q 10 8 6 5 3
K J 9 6 5 3
Q J
Q 9 8 4 3 Vul: E-W
------ Opening lead: ace of clubs

NorthEastSouthWest
2 * Dbl
4 5 5 Dbl
Allpass

* Alerted, though I don't believe it needed to be.

South should probably have redoubled here. Well, it is a close decision, one where it's not altogether clear who's bidding to make, who to sac. Still, South has slightly better distribution with a 5-card side suit and a void than would be the case with a 4-card side suit and low club. Lemme give a few tidbits on the scoring. Redoubled, 5 spades without an overtrick would beat any undoubled little slam -- by 20 points. If there is an overtrick, you lose to the doubled slam -- by 10 points, but of course whip anyone in an undoubled slam. (That's this hand, non-vul major suit. Please don't generalize beyond that.)
It's not really a slam hand. One person bid and made it, however -- doubled. Two trump leads from West would have queered that slam attempt. But the lone slam bidder got a heart opening lead, screwed his courage to the sticking point, took the finesse and he was off and running. He lost a diamond and now proceeded to ruff out the suit for his 12th trick.
But of course the redouble means you've got to make the hand, which this declarer neglected to do. Indeed, it looks to me as though this declarer, also without a trump opening lead, could have effected the same 12-trick line as the other fellow. But she was in five on the A of clubs opening lead without much need to pick up a 12th trick. And from there, she shilly-shallied around until she didn't even have an 11th trick.
Take a look at the hand after trick one. And do you see what I see? It looks as though (with that lead) that the hand works out easiest for 11 tricks by playing from dummy. The king of clubs is now high, and let's even assume that the heart finesse is off. So the first two rounds of hearts will be the Q and J from the closed hand and two small from dummy. You're always going to lose that diamond, so dismiss it from mind. Spades are solid. You've got just one small heart and two small clubs to ruff in the closed hand (i.e., if the heart finesse is off). You've got five trump left. On a 2-1 split, the hand is cold for eleven tricks!
Now let's go back and take note that the heart finesse is going to work! That means we don't have to lose a heart, doesn't it? Or does it? For now what we see is two low hearts and two low clubs to be ruffed in the closed hand, and after two rounds of trump you'll only have three trump. So you're still going to lose a heart. It doesn't matter where the king of hearts is (i.e., going for 11 tricks. Going for 12, of course it does). Indeed, an uneven spade split is a far greater danger to the hand than the heart finesse. So at trick two, cash a high spade and when everyone follows, the contract is assured.
Lemme take another look at dummy. After ruffing the ace of clubs opening lead, you figure that'll allow you to sluff a heart on the king of clubs and avoid the heart hook. So you cash the king of clubs, sluffing the queen of hearts and later lead the jack, covered, to the ace. Do you see what I see now? You've now got three low hearts instead of one plus two low clubs to be taken care of with the closed hand's five trump, while two rounds of trump must be taken! The hand is in a far more parlous situation side-stepping the heart finesse, not less.
This is just what this declarer did, and she'd just shot herself in the foot. She'd made the not-too-rare mistake of thinking (though doubtless not consciously) that eliminating a loser would mean the creation of a winner, which isn't always the case. Nor was it the case here, largely because in sluffing the queen of hearts on the king of clubs, she'd sluffed a winner, not a loser. (Actually, it looks to me as though this declarer could still have effected the same line to 12 tricks as the successful slam bidder. Instead of two heart winners, a long diamond and 9 trump through ruffing 3 times in dummy, she'd have one heart, one club and one diamond plus the same 9 trump winners. And certainly she still had a successful line to 11 tricks through cross-ruffing. So to say she had at that point shot herself in the foot is a little premature. But for the line she took, she had effectively done so, had weakened her holding in sluffing a heart honor, not improved it.)
So here's how the hand played out: ace of clubs, ruffed, spade to the ace, king of clubs, sluffing the queen of hearts, spade to the jack (!), jack of hearts covered, ace winning, ruff a heart, diamond queen to the ace, club lead from West ruffed, diamond ruffed, heart ruffed, diamond ruffed, heart to the 10 (!) and now the 3 of hearts (!) took the setting trick! Declarer had to get rid of that queen of hearts to allow the 10 and 3 of hearts to beat her?
Incidentally, where I said she could certainly have cross-ruffed out for 11 tricks, it would have been necessary to count just a bit. By eliminating the potential for two heart winners, she'd cut herself down to one club and one heart winner in the side suits (unless she ruffs out three diamonds and has an entry to the last one). And if you've only got two side suit winners, then you need nine trump winners for 11 tricks. Which means you can't draw two rounds of trump, for 6 spades in the long hand plus two ruffs in dummy only comes out to eight. You have to get three ruffs in dummy -- which means you can't lead trump a second time until you've got your 3 dummy ruffs tucked away.
But, as already made clear, the real harm came in sluffing the queen of hearts on the king of clubs, a card she could well have used later.
Of course, the category here is redoubles and I'd like to return to that theme before leaving. Yes, of course hindsight is better than foresight, and I'm well aware of how easy it is to say such-and-such a bid (or double or redouble) should have been made and indeed have more than once felt a sense of distaste as someone loftily announced what should have been bid from the high ground of looking at the whole hand.
But having said that, I can only say that a redouble from South looks as safe as many a game, and many a slam bid, or safer. Of course you don't know that your partner's points are going to be where you want 'em, or even if his hand will be as strong as indicated. But how often do we know that a bid is safe and cannot turn out badly? So I've indicated the points available, which are more than an undoubled slam, and can only say that a redouble with an apparently good fit, a five-card side suit and a void looks to be a very attractive chance to take.