7 no trump
Perhaps South's cue bid in spades was unwise, especially in view of his partner's weird leap to six in that suit, and his unrealistic push to a grand slam after Sims bid six no trump, trying to extricate himself from six spades.
East was guilty of avarice when he doubled six spades. He was to pay dearly for it. From the sound and fury of East's doubles, West's lead of a spade was entirely logical.
Sims counted 12 tricks: five hearts, five clubs and two spades. A successful spade finesse would produce the 13th—but it was impossible that the spade finesse could succeed. Sims had to find another way of pulling a rabbit out of the hat.
He took dummy's ace of spades and king of spades, discarding diamonds from his hand. Then, playing swiftly as he always did, Sims cashed his five club tricks, discarding a low spade and the lone diamond from North's hand. Now he was ready for the hocus-pocus. He cashed his heart ace, "accidentally—on purpose" playing dummy's 4. He played his heart jack, overtaking with dummy's queen. And he continued leading down the hearts until dummy remained on lead with the lowly 3.
East knew, of course, that South had another heart. He knew, too, that South did not have a spade. So he threw away the queen of spades in order to hold his ace of diamonds, expecting that South would win the last heart trick.
But East had taken his eye off the ball. When South produced his last heart, instead of being one that would win the trick and force him to surrender a diamond to East's ace, it was the lowly deuce—small enough to crawl under dummy's 3. So North, not South, won the 12th trick. And North, not East, won the vital 13th that brought home the grand slam.