156 - A solução do post #136.

Black did move his King (what else?) From a7 (where else?)

On a7 he was under a seemingly impossible check by wBg1. In fact this check was a discovered check, and the discoverer has now disappeared. It has disappeared because it has just been captured by the black King. Ergo it was a wN.

Last move was -1. Ka7xNa8, after Wh. played Nb6-(x)a8.

in The Chess Mysteries of Sherlock Holmes, Raymond Smullyan, 1979