Late one night, a blazing inferno destroys the home of a well-to-do English doctor. Tragically, the man's wife perishes in the flames. Arson is obviously the crime, but after digging around, Inspector Pitt isn't sure who could have set the fire. Enlisting the aid of his wife Charlotte, Thomas searches the dank London streets for a killer, puzzled by the question of whether the true target was the doctor's wife, or the doctor himself.