White to play, Kharlov–Ernst, Haninge 1992. Black’s last move, g6-g5 was a decisive mistake. Which move did White play to exploit it? Answers should be emailed to chess@spectator.co.uk by Monday 31 May. There is a prize of £20 for the first correct answer out of a hat. Please include a postal address and allow six weeks for prize delivery.

Last week’s solution 1 Ng5+! and mate followed after Kd6 2 Nf7+ Kc5 3 Qf2+ Kc4 4 Rd4+ exd4 5 Qxd4#

Last week’s winner Catherine Moorehead, Kingussie, Inverness-shire