Chess Puzzle of the Week (161)

My book Chess Puzzles for Heroes (let me know if you want a copy) includes a chapter called Spot the Blunder, in which the reader has to find the plausible but erroneous move played in the game.

This is a Spot the Blunder puzzle from the game Penrose – Aitken (Enschede Zonal 1963).

The position is level at the moment, but Black managed to find a losing move. Can you do as badly yourself?