East overtook with the jack but South ducked. The continuation of the queen, perforce, drove out the ace as West contributed the three. South led a spade to the ace and followed with the jack finessing East, the danger hand, for the queen. West exited with a heart for dummy's jack, Declarer unblocked the king of spades, crossed to the ace of hearts and finished the spades, discarding a heart and a diamond from hand. A diamond to the queen was topped by the king but an overtrick was home, N-S +630. Declarer had performed well by declining to win the first club. At this vulnerability, it was quite possible that East had pre-empted with a six-card suit and South will be in a world of trouble if he wins the ace of clubs.
Declarer was constrained to finesse East for the spade queen for fear that East might regain the lead and cash the club winners.
South should have offered a takeout double instead of overcalling 3NT. North would have leaped to four spades, in this scenario, where eleven tricks would have been available by playing West for the queen of spades.
East's pre-empt at favorable vulnerability was a good plan and was successful by driving N-S into the wrong game.