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

¹ A direct 4♥ rebid is an option

West leads the ♣Q.
How should South play?

Solution

South counts four (possible) losers: the ♠A, two clubs (in view of the lead the ♣A is certainly with East) and a diamond (if the ♦K is with West).
If West has the ♠A, South can pitch the ♦Q on North's second high spade.
South can 'combine' his chances: he can make the contract if either the ♠A or the ♦K is favourably placed, provided he can investigate the position of the ♠A first. Only after the ♠A should turn out to be with East, would he risk the diamond finesse - as his second and last chance. He must therefore prevent - if possible - EW from forcing the diamond finesse upon him prematurely.
This is the lay-out he has to concentrate on (if the ♦K is with East, declarer will always make his contract; if both the ♦K and the ♠A are wrong, he will always go down):

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

It is imperative declarer ducks the lead in dummy to prevent East from gaining the lead in clubs.
- If West continues with a small club the problems are over: South again ducks in dummy, East has to win with the ♣A (to prevent South making the ♣10) and declarer later discards the ♦Q on dummy's ♣K.
- If West continues with the ♣J (better defence), declarer again ducks in dummy. He ruffs the next club (West has no choice) and at once plays a spade. If the ♠K wins the trick, he crosses to the ♥A and plays another spade. West will probably win with the ♠A and later declarer enters dummy with the ♥K and pitches the ♦Q on the ♠Q.

Why is it imperative for declarer not to cover the lead of the ♣Q with the ♣K? Because if he does cover, East wins with the ♣A and switches to a diamond, forcing declarer to finesse. This way declarer cannot profit from the favourable position of the ♠A.
Why does declarer have to play a spade at once? Because if he draws trumps first and plays spades later, he will be locked in dummy since West will duck the first spade trick.