This hand, reported to me by Khokan Bagchi, was easy to bid. The 2NT rebid was 18- 19 and 4D was minorwood.
4NT showed two keycards without the queen of trumps and South bid the diamond slam. West led the 2C, which was third or fifth best, and declarer played the 10C which held. Before reading on, consider what card you would play at trick two?
The secret to the trick two play is seeing the line for twelve tricks. Declarer played a trump to the ace intending to play another trump. After two rounds of trumps, the contract is cold on any 2- 2 or 3- 1 trump split since declarer can just play winners and take ruffs and the defender with a third trump can ruff at any time but there is no further defence. It’s not correct to play to the 9D since, if that loses and you draw two more trumps, you need hearts to be 3- 3 which is only 36 per cent. If you don’t draw the third trump, you are exposed to an over ruff in later play. To your horror, West discards a club on the AD and you need a trump endplay to make 6D.
The required three card ending is shown in the second diagram. On the third last trick, North plays a small diamond, East wins but is endplayed into returning a trump.
We can reach this ending with two distributions. If East is 2443, we can ruff two hearts and one spade to set up the endplay. If East is 3343, we cannot ruff two spades since we won’t have 3 trumps for the ending. We need to finesse East for the king, ruff the third spade and one heart before the endplay. Which line should you take?
The answer, of course, is to combine the lines. Play KH, AH and ruff a heart. If they are 3- 3, go to the KC, take the spade finesse then AS, AC and a spade ruff before the endplay.
If the hearts are 2- 4, then play AS, spade ruff, KC, 2nd heart ruff, AC ( throw the last heart) and ruff a spade to effect the endplay! I will leave the other 4- 0 split to you as an exercise!