After this hand Colin said he was going to publish it on the Bridge Base Forums, to see if anyone agreed with the way I bid. I like my bidding, even though the result was a disaster.
Colin had the big hand sitting South. He opened 1♠, and I shrewdly repied 2♦. Next Colin showed his big hand, and at least 5-4 shape with a leap to 3♥. Sitting North I now knew big things were happening. A massive double fit.
I reflected for a while then pulled a bold 5♥ bid out the bag.
It sets Hearts as trumps, shows slam interest, and asks partner to bid the slam with good trumps (two of the top three honours). This wasn't something we've previously agreed, and when the opponent asked Colin the meaning he said "No idea" but swiftly bid six anyway, which turned out to be the right thing to do. 6♥ is an excellent contract.
When Colin saw this dummy I expect he was rather surprised, probably thinking we should be in 6♠.
West led a club, which Colin took with the Ace. Then he crossed to the ace of diamonds and tried to go back to dummy's ♠K, with the plan to throw away a Club. Unfortunately East ruffed this Spade, cashed a Club, then got another Heart trick later on. The result, 6♥-2 was a bottom. The rest of the field were either in 6♠= or 4♠+2. Why was no one in Hearts? Don't they realise a 4-4 trump fit is better than a 6-3?
Whatever the contract, if Spades split there's 11 top tricks, and you can easily get one more by force in hearts. Either slam should be fine.
Although I was slightly worried about suit quality in 6♥ that doesn't mean it should't be trumps. If there's a suit we've each got four of then if we're not strong in that suit we're usually not making any slam. Actually on this layout in 6♠ you've got a trump loser but can discard two Hearts and a Club on dummy's Diamonds, and with the Heart finesse working you only lose one trump. In 6♥ you have no Spade losers (barring a defensive ruff) so make if you only lose one trump.
In summary, I stand by my bid, it was just an unlucky deal. However it was a poor result and with this some other misadventures we didn't trouble the leaderboard that night.