Neither Side Vulnerable. West led Jack of Diamonds.

Most if not all of us have sat opposite a partner who loves to bid all of his or her values, sometimes two or three times. After our North player tried to accept her own slam try, South found himself breathing the rarified air of the five level, needing some skill to bring five hearts home.
 
South overcalled the opening bid with one heart, and West preempted to three diamonds. North judged her hand too good for a 3 or 4 heart bid, and the four diamond call was a "last train" type of slam try, showing a heart fit and great strength but not necessarily anything specific about diamonds.
 
Having made her try, North could have prudently subsided when South signed off - after all, the king of diamonds was very likely to be in the wrong offensive hand, and the original overcall was non-vulnerable and at the 1-level. But North pushed past the matchpoint game, hoping for luck and 2 key cards from South. Whoops! North finally applied the brake.
 
The play went quickly. East won the ace of diamonds and cashed the queen before exiting with his six. Declarer ruffed the 3rd round with dummy's six of hearts, and with a typical flair for drama played the two of hearts from dummy, covering East's four with his five of hearts.
 
How did South know the "deep finesse" was a winner?  From the bidding, it was virtually certain that West started with 5 diamonds, leaving only 3 for East. East-West were playing 5-card majors and "better minor", so her diamond bid on 3 cards meant that East would hold 4 cards in each major, and a doubleton club. Having an exact count on the hand and sufficient entries, South repeated the trump finesse twice more and made the shaky contract by way of four heart tricks, a diamond ruff in dummy, four club tricks and two spades.

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