You play 7S from the South hand (after a transfer sequence) on the Spade 2 lead.  What is the best line for the contract?

This hand is from the Portland Pairs 2004, played and analysed by Jeff Smith.

At first glance, there are 12  top tricks and extra chances are: KC finesse or KD finesse or drop KC in 3 rounds and KD finesse, or a very unlikely C/D squeeze (which needs West to hold DKJ and KC) .
On the actual hand, West held S 1052 H 843 D K98 C KJ97 so none of these would have been successful.

However, best of all is the dummy reversal line which only depends on a 3-2 trump break and does not invalidate the other chances if trumps are 4-1.
The play goes win  9S, AC, ruff club, back to KS. If either opponent showed out here, you draw trumps and revert to guessing which finesse to take (the squeeze is no longer possible).
Both opponents followed, so ruff another club, back to KH, ruff the last club, back to AD, draw last trump and enjoy all the hearts...that's 3 trumps, 3 ruffs, 5 hearts, AD & AC for 13 tricks.

This board helped Jeff Smith and Jackie Pye to second place overall.