A female killer stalks the streets of London, sleeping with young men before slashing their throats and mutilating their bodies. The crimes have baffled the police and enraged Londoners, who demand the murderer’s arrest. Mary, Duchess of Dove, a gentle young widow who is beloved by all who know her, seems an unlikely suspect, but the clues all point to her. The police have a variety of theories — perhaps the Duchess has been hypnotized or drugged, maybe she has an evil double, or could it be a Communist plot to discredit the peerage? Inspector Basil Icelin is determined to solve the mystery, but the true explanation is far more shocking and terrifying than anyone could ever imagine.