The second unbelievable contract from my personal collection is this curious slam from a Christmas drive (MP scoring). My partner was Elly Maaswinkel.
In the past we had played together regularly but even then our bidding had been common sense, we hardly had made any agreements.
Now, after an interval of many years, we really had nothing else to go on but common sense.

On this deal west dealt this a heavy blow.
I was south, holding:

¹ strong hand or weak two in diamonds ('possibly extremely weak', east said)

What should I bid?

If Elly's double was a 'normal' take out double (on a diamond opening bid), I could press a little by bidding 2NT (surely she had a spade stopper). But was it?
When bidding over an opponent's multicoloured opening it is rather customary to assume him to hold the weak variety, in this case the weak hand with a diamond suit. If Elly thought this way she would have bid 2♦ here if she held a hand suited for a take out double on a natural weak 2♦-opening. As a consequence the double on 2♣ then showed primarily a club suit here (lead directing double). Her hand could vary in strength then.

So I bid 3♣, the obvious choice if her double was lead directing; with extra strength she could now bid on.
And if the double would turn out to be purely for take out after all, we still could get to 3NT after my voluntary 3♣-bid (it showed some strength after all).

West passed, Elly bid 6♣ (!) and east passed.

Should I correct to 6NT? No, that would be inconsequent. Elly knew as well as I did the scoring was MP. So I assumed she held a strong distributional hand and a long club suit and I passed.
West lead ♠3.
When dummy went open, I saw I had been wrong all over...

E/NS		♠	A K 8 2
		♥	A K
		♦	K 7 6 4
		♣	A K 5
		♠	6 4
		♥	J 5 4
		♦	A Q J 3
		♣	J 9 6 2

¹ strong hand or weak two in diamonds ('possibly extreme weak', east said)

West lead ♠3.
Not a great auction, to say the least. A crazy deal by the way: on seeing the NS-hands only, one would deem 6♦ a reasonable slam. But by way of his ludicrous 'weak two' (on ♦109852!) west had given away the diamond suit was 5-0.
It looked like 6NT hardly had any chance at all, though our combined point count was 33. 6♣ even had to be worse in view of that ridiculous 4-3 fit.
On second sight: both 6♣ and 6NT make if ♣Q10 were bare. I would then score close to a bottom because almost every other NS-pair was bound to end up in 6NT.
But if I were to lose one club trick and score three, both 6NT and 6♣ would go one down. That would mean a middle score...

I won with ♠A, east signalling with ♠Q. I could not try to ruff a heart because after cashing ♥AK I would not be able to cross to my hand (a diamond would be ruffed by east, whereafter EW would start a cross-ruff in spades and diamonds).
So I cashed ♣A (east ♣3, west ♣5; no ♣10...), ♣K (east ♣10, west ♣7) and played ♣5. East won with ♣Q and west followed suit with ♣8.
East played ♠B back to dummy's ♠K, west discarding ♦2.
The fortunate club distribution meant I would go one down, just like those playing 6NT, because I saw only one more loser, a heart. I would even win the contract if ♥Q was single or double. I hoped not, because then 6NT would make as well. A quick count showed however ♥Q would not drop: west had 1-4-5-3 and east 6-4-0-3.
Was there any other chance to make the contract? Yes, if east had ♥Q, I could squeeze him in spades and hearts, since he controlled both major suits then. I would have to cash the diamonds now. After two tricks in spades, three in clubs and four in diamonds east would still have to find a discard in this situation:

O/NZ		♠	8 2
		♥	A K
		♦	-
		♣	-
♠	-			♠	10 9
♥	10 7 6 3			♥	Q 9 8
♦	-			♦	-
♣	-			♣	-
		♠	-
		♥	J 5 4
		♦	-
		♣	J

It did not even matter in which hand I would end up.
If east threw a heart, I would cash ♥AK, ruff a spade and cash ♥J.
If east threw a spade, I would ruff a spade, cross in hearts and cash the good spade.
Yes, a trump squeeze.

Because I knew east and knew he would take it well, I came with this macho-claim after trick five (I was in dummy with ♠K): 'If you have ♥Q, I make the contract; if you do not have ♥Q I will be one down', whereafter I gave my line of play.
While east considered my claim, I reviewed the whole deal:

E/NS		♠	A K 8 2
		♥	A K
		♦	K 7 6 4
		♣	A K 5
♠	3			♠	Q J 10 9 7 5
♥	10 7 6 3			♥	Q 9 8 2
♦	10 9 8 5 2			♦	-
♣	8 7 4			♣	Q 10 3
		♠	6 4
		♥	J 5 4
		♦	A Q J 3
		♣	J 9 6 2

How about 6NT? West would lead ♦10. After three clubs and the ♠Q-return, declarer would make his contract by way of a Vienna Coup: declarer unblocks ♥AK (!) and cashes the diamonds (ending in his hand) and the fourth club (in dummy he discards ♠2).
Again east would still have to find a discard in this situation:

E/NS		♠	K 8
		♥	-
		♦	-
		♣	-
♠	-			♠	J 10
♥	10			♥	Q
♦	10			♦	-
♣	-			♣	-
		♠	6
		♥	J
		♦	-
		♣	-

Pity, 6NT makes as well. A bottom after all? No, not every south will follow that line of play, so perhaps I would get a middle score and...
Wait! South would not be declarer in 6NT! North would! If east passes like on our table (few players open a weak 2♠ holding a four card heart suit) the bidding will begin north 2♣-south 2♦; north 2NT. East will of course lead ♠Q and after winning a trick with ♣Q he will continue with a spade. The Vienna Coup is off then: north's spade entry, essential for that technique, has been removed.

So I would score a top, thanks to this ridiculous 4-3 fit in a minor while scoring match points! 6♣ was the only slam that made!
That is to say, if east held ♥Q...

At last east had come to a conclusion: slowly he screwed the cap from his fountain pen and started filling out the score slip. I looked over his shoulder... +1370 to NS!
It was like a chess player laying down his king.
And yes, it was a full top: the usual contract was 6NT, usually one down, sometimes two.