S/EW		♠	A 10 8 6 5 4 3
		♥	4 3
		♦	K 10 7
		♣	6
		♠	Q J 9 7 2
		♥	9 8 2
		♦	A J 2
		♣	A J

¹ Splinter: singleton or void in clubs, good spade fit, slam invitational
² Control bid
³ No control in hearts

West leads the ♥A (East the ♥10), continues with the ♥K (East ♥7) and then plays the ♥J.
How should South play?

Solution

Declarer has lost two heart tricks and is in danger of losing a trick to the ♠K now, despite having twelve spades in the combined hands. After all, East is out of hearts and if he has the ♠K, that card is now promoted. After losing a trick to the ♠K, declarer may subsequently also lose a trick to the ♦Q.
He can ruff with any low trump in dummy. If East does not have the ♠K, the contract is safe. If East overruffs and plays back a club, declarer may still locate the ♦Q.
However, some players hardly ever find a queen. For instance Peter found his last queen in 1974 (Ed exaggerates, as usual: as late as 1982 I found a queen and I am still married to her, -Peter).
There is a better line of play, especially for players like him.

S/EW		♠	A 10 8 6 5 4 3
		♥	4 3
		♦	K 10 7
		♣	6
♠	-			♠	K
♥	A K Q J 6 5			♥	10 7
♦	9 6 4			♦	Q 8 5 3
♣	K 7 5 4			♣	Q 10 9 8 3 2
		♠	Q J 9 7 2
		♥	9 8 2
		♦	A J 2
		♣	A J