Inspector Lestrade of Scotland Yard brings Holmes a mysterious problem about a man who shatters plaster busts of Napoleon. One was shattered in Morse Hudson's shop, and two others, sold by Hudson to a Dr. Barnicot, were smashed after the doctor's house and branch office had been burgled. Nothing else was taken. In the former case, the bust was taken outside before being broken.

Holmes knows that Lestrade's theory about a Napoleon-hating lunatic must be wrong. The busts in question all came from the same mould, when there are thousands of images of Napoleon all over London.

The next day, Lestrade calls Holmes to a house where there has been yet another bust-shattering, but there has also been a murder. Mr. Horace Harker found the dead man on his doorstep after investigating a noise. His Napoleon bust was also taken by a burglar entering through a window. It, too, was from the same mould. Also, a photograph of a rather ape-ish-looking man is found in the dead man's pocket.

The fragments of Harker's bust are in the front garden of an empty house up the street. Holmes concludes that the burglar wanted to see what he was doing, for there is a streetlamp here, whereas the bust could have been broken at another empty house nearer Harker's, but it had been dark there.