Dominique Sorelle's mutilated body was found one night, hanging from the Austerlitz Bridge in Paris. The Government enlists Gerard de Montclaire, France's most acclaimed detective, to find the killer. The murderer may have committed other, similar crimes. There is growing alarm in official circles, hinted at in the tabloid press, that a "Ripper" is loose in Paris. The investigation takes Montclaire and his associate, Sir Francis FitzMaurice, into the dark world of Parisian sadism, in search of an insane but clever killer. What they find is a conspiracy that frightens the Government and stymies Justice. Can the great detective get justice for Dominique Sorelle? Or, is this to be his greatest failure?