I played this hand a few hours ago on BBO. See handviewer: http://www.bridgebase.com/tools/handviewer...KH9D5HTSAHJDJHK
I sat north. I assumed partner's 3NT was gambling but didn't know. Whatever it was, I wanted slam. 4 clubs was either Gerber or "pass-or-correct". 4 diamonds showed partner's suit. Hoping for partner to have either the spade queen or heart ace, I bid 6 spades. Partner, bless him, raises to 6NT, and I decide to pass and let him go down one or two undoubled, but then it gets doubled and I think it's better to go down one in a suit than four or five if they can run hearts. So I bid seven clubs, that gets doubled too, and all pass.
I can't recommend partner's bidding -- a dubious usage of gambling 3NT and a ridiculous takeout of 6 spades when he had plenty of spade support.
East leads a small diamond and I think there's no way he underled the king (or I can't risk that he did) so I put up the ace. Then a spectacular "poorbridge" moment: I lead the queen of diamonds, planning to discard a spade from hand if west plays a low diamond!
I didn't ponder how incredibly stupid this was: if clubs break in my favor, I have 13 top tricks. But before I had the chance to whack myself in the head, west made an even stupider play: he ruffed low!! Apparently he didn't think east would underlead the king of diamonds either.
Of the 15 other pairs, 8 played in 6 spades, 2 in 4 spades, 1 in 7 spades, 1 EW in 7 hearts doubled, one in 4 hearts doubled, and...one NS in 3 clubs, down one!
6 spades is easy to make if you want only 6. The logical play for 7 spades, taking AK of clubs and ruffing a club with dummy's 8, falls to the adverse break of clubs.
GIB shows that east can defeat 7 clubs double dummy only by leading a spade. I analyzed that dummy wins the spade queen, leads a club and west covers, so south wins and returns a heart to dummy to lead another club. This time west does not cover, and declarer is busted. If he wins in hand, he loses a trump later. If not, he cannot return safely to hand because west will ruff a spade.
The poor fellow who went down in 3 clubs won a diamond lead with the jack, led trumps to his AK, then gave up on drawing trumps. He played a spade to the queen, and the diamond ace was ruffed and overruffed with the club five. At this moment declarer can win the jack of trumps, throw west in with the ten, win the heart return and run spades for 12 tricks. Even if he doesn't know the distribution he could win a spade return too, no problem. Instead he puts down the queen of hearts...and loses to west's king! Now a heart return to the ace, diamond ruff by declarer, ace of spades ruffed by west, heart ruffed by declarer, another spade ruffed by west, and finishing with two good hearts for the defense. Oh dear.
Handviewer link: http://www.bridgebase.com/tools/handviewer...TSTHJD4DKDQH5SJ

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The bidding:
E - S - W - N
P - 3NT - P - 4♣
P - 4♦ - P - 6♠
P - 6NT! - P - P
X - P - P - 7C
X - AP