Malfeasance A-plenty

Q 9 3
A Q 8 5
A K J 9 8
6
6 K 10 8 7 4
J 6 3 2 10 7 4
6 5 3 7
A K 10 7 3 9 8 5 4
A J 5 2
K 9
Q 10 4 2 Contract: 6 diamonds
Q J 2 Opening lead: A of clubs

This moderately interesting hand became far more so when I ran through all the different types of malfeasance. Let me start with a double: West cashed the A of clubs and switched to a low heart, low from dummy, low from East, the K from declarer. The K from declarer? Yes, indeedy. He didn't notice that he could've won with the 9, which sets up the whole hand. (Playing from dummy, declarer could've sluffed two spades on the hearts and taken the spade hook. But wait a minute. Had East gone up with the 10, couldn't declarer then have finessed the 9, a cover by West doing the defense no good? Yes, certainly. The 8 then becomes a valuable card. But at least you put declarer to a guess.
One declarer even went down in a five bid, which would make even with a losing spade hook. How'd he do that? Well, lemme see. Opening K of clubs lead, shift to a diamond, which declarer carries out to the third round and then finesses the J of spades. Now he goes back to dummy with the A of hearts and leads the Q of spades, covered by East. (A poor play by declarer, banking on defensive stupidity, as opposed to the possibility of a K doubleton with East. We can see that that wasn't the case, but it doesn't augur well for declarer to look for a stupidity rather than a winning layout.)
Now he unblocked the K of hearts and used a trump, that's a fourth round, now, to get to dummy. And that's where he lost his third undertrick. It wasn't wise to block the suit in the first place, but once he did, he had two ways to get to dummy: lose a spade, which he's going to lose eventually anway, or lose a club, and ditto. Using a trump entry gets him to the Q of hearts a trick sooner, but costs a valuable trick to do so. For now what's he going to do with the fourth round of hearts?
Well, what he's going to do with it is lead it, sluffing a spade, letting the 10 win. That's not too bright. So he wound up losing one club, one spade and one heart.
And then there's the handling of those clubs on the A of clubs lead. The lead doesn't guarantee the K, of course. Howevwer, there were a few declarers who made a six bid banking on that presumption. With the Q J, you ruff out the K and later sluff a spade on the second honor. But take a gander at what declarers and defenders did with that. One declarer played the J under the A! Oh, that'll fool 'em, won't it? Heh, heh, heh. But now he has no leverage. West can just sit back with the tenace over the Q of clubs, get out with a trump (or spade) and wait for the setting trick to jell.
One declarer, after getting out trump, led the J, and when uncovered, ruffed, losing that chance for a 12th trick. If he led the suit, it shoulda been the Q, for he wants a cover, and indeed, some West's were covering the second round of the suit, handing the contract over. And one defender, when the hand was played from the opposite side of the table and the Q J 2 were showing, captured the lead of the Q with the K appropriately enough, and now with the A 10 tenace over the J, when he could've just waited for the setting trick, tried to cash the A. Bid and made. A slam. It may be true that that defender doesn't know declarer has a singleton in the closed hand, but look at that dummy (the closed hand above) and ask how he's going to sluff a second round club loser if he has one.
Oh, there were many opportunities lost and tricks handed over. With the opening lead of the A of clubs, declarer (in slam) needs the spade hook to be on, and either the K of clubs to now be sitting over the Q J, allowing a valuable winner to be developed there, or extraordinary luck in hearts, dropping the J and 10 in three leads. And the funny thing is, these can be tested sequentially. It doesn't hurt declarer to take three rounds of trump, then three rounds of hearts, noting that there's no help there, then the spade finesse and now the Q of clubs, intending to sluff a spade if not covered. And you've got to have the courage of your convictions. Do it. Declarer would have an entry to the last club honor on the fourth-round ruff of a heart. But if the reader can see another path to a winning slam from declarer's viewpoint, please let me know.
Oh, and one more possibility: that East has a K doubleton of spades. It was a serious mistake to throw the J of clubs on the opening lead, which does nothing but weaken declarer's hand, and a mistake, once the J of spades held, to go back and lead the Q, which will almost surely be covered, and of course a mistake not to try the various possibilities . . . all of which could have been tested in sequence, without wiping out the potential of the others: Three rounds of trump, three rounds of hearts, spade hook winning, cash the A, no K falling, Q of clubs, ruffing out the K if covered, sluffing a spade on one of those club honors, anyway, and now a third round of spades can be ruffed in dummy, a fourth-round of hearts in the closed hand for access to the lone club winner.