This is either a question of too much science or too little, in the bidding.
Here's the hand and the actual auction:
Nevertheless, I open 1C. Lefty overcalls 1S and partner bids 2D. This is, of course, music to my ears.
Probably best at this point is 4NT, RKC for diamonds. But I decided that I'd wait to see where partner's 10+ points were. So, I made the only other forcing bid available to me. I bid 2S. First mistake: too much science. Just check for aces already. Partner would have bid 5S (2 aces + queen of trumps). And we'll be in 6D. If partner has zero or one ace, he bids 5C or 5D and we are not too high.
Anyway, I bid 2S and partner trots out 2NT. From his point of view, my 2S is a search for 3NT. He is telling me that he has spade stoppers. From my point of view, this is the worst possible news. If partner has KQ of spades and a smattering of heart and diamond honors, 5D is the best we can do. I duly bid the diamond game. Second mistake: too little science. I still had Gerber (4C) available to me. I could have cheaply checked for aces by bidding 4C.
Anyway, 5D making 7 was a near-bottom. All the new partnerships bid the slam.