South can make six clubs. The first crucial play goes against the grain of normal technique: the diamond lead must be won in dummy with the king (or ace), then a second diamond is won with the queen. It is impossible to succeed if you win the Q first.
South leads four rounds of clubs to reduce everyone to seven cards in the diagram. Next comes the 10, throwing a spade from North (East throws a heart); then:
1. If West throws a spade, win the A, ruff a spade, and lead your last trump. West must throw a diamond else you can duck a heart. North throws a heart, and so does East. When you cross to the A, East is caught in a vice squeeze: he must discard a heart to protect the 8, then a heart lead will establish the 8 as your 12th trick.
2. If West throws a diamond, lead another club, throwing a spade from North (West throws a spade, East a heart). Next lead the 8, your last trump, then:
a) If West throws a spade, throw a heart from North. Win the A and A to bring about the same vice squeeze against East.
b) If West throws his last diamond, jettison the A from North! Now lead the good 8. West must throw a spade (else you can duck a heart) and the vice squeeze appears once again.
3. If West discards a heart, just duck a heart.
Note that in all variations, West was forced to hold on to the A-7.