In 1930s London, famed psychiatrist Anselm Rhys is found dead in a locked office. There is no evidence, no witnesses, no murder weapon. The Scotland Yard detective leading the investigation turns to Joseph Spector, a retired magician turned detective. Spector has a knack for explaining the inexplicable, but even he finds this case very strange. After interrogating the psychiatrist's patients and household members, he learns their dark secrets, each of which could be a motive for a crime. When a second mysterious murder occurs, this time in an elevator, the detectives realize that they urgently need to stop the criminal.