When there is a competitive auction, it is very difficult to bid slams with any accuracy. The hand shown, from a recent club session, is such a hand. Looking at the hand, we see that EW would like to reach 7H, which is an excellent contract and does not need the club finesse. On the other hand, NS would like to sacrifice in spades over both 6H and 7H with the latter penalty of 1100 being much cheaper than the vulnerable slam. Still the hand seems to have caused considerable problems since two pairs played 4H, three played 5H and only one played 6H. Most Easts will open 1NT with their partners announcing 15- 17. South probably overcalls 2S showing spades and a minor. West will bid 3H which is game forcing ( competitive heart bids will start with 2NT, Lebensohl). North, with a weak hand, will make a LoTT- based raise to 3S since NS appear to have a 9 card spade fit. East has a clear 4H bid and South, with a sixth trump, bids 4S. South feels very safe since the long club suit should be easy to develop.
West now has to show some insight. It is likely partner has no high cards in spades since the opponents obviously have 10+ between them. Thus, in the other three suits, West knows that EW have a minimum of 15 plus 13 points. This is a minimum of 28 of the 30 points in those three suits so at most a queen is missing and there are no spade losers. It should be clear to West to bid the small slam emphasising diamonds on the way. When West passes over 6S, it shows no first- round loser and East can revalue the QD and bid the grand slam. Now we return to how to play 7H. The lead will be a spade ruffed in dummy. Since the trump and diamond suits are completely safe, the only question is where the losing club goes. The answer is that it is discarded on the long trump. Which long trump you say? Cross to the AH, ruff another spade and then draw trumps throwing the 3C on the last heart.