Last week’s puzzle was taken from In The Zone, a new book by the prolific Cyrus Lakdawala: you can read my review here.

This is taken from a game between Edmar Mednis and Bobby Fischer, played in the first round of the 1963-64 US Championship.

Mednis has a strong passed pawn and could have won here by playing 24. Rd5 Rxe7 25. dxe7 Nc6 26. Nd6 Nxe7 27. Nxc8, with two rooks and a knight against Fischer’s queen. Instead he traded queens with 24. Qg5, exactly the sort of pathetic move I would have played. Bobby eventually rounded up the d-pawn and won the ending – followed by his next ten games, finishing the tournament with an unprecedented 100% score.

If he’d lost this game, as he should have done, chess history might have been very different.

Many thanks to all who analysed and commented on Facebook – including two IMs!