White to play. Gaprindashvili–Servaty, Dortmund 1974. The dark squares around Black’s king are critically weak, and White found an accurate way to conclude the attack. What was her winning move? Answers should be emailed to chess@spectator.co.uk by Monday 20 September. There is a prize of £20 for the first correct answer out of a hat. Please include a postal address.

Last week’s solution 1 d6+! Rxd6 2 Bb4 won rook for bishop, and the game soon after. But not 1 Bd4? Nxd5 2 Re4+ Re6 and Black is safe.

Last week’s winner Emmett Smith, Caterham, Surrey