Amid the hustle and bustle of the Paris 1889 Universal Exposition, workers discover the mutilated corpse of a popular model and Moulin Rouge Can-Can dancer in a Montmartre sewer. Hysterical rumors swirl that Jack the Ripper has crossed the Channel, and Inspector Achille Lefebvre enters the Parisian underworld to track down the brutal killer. His suspects are the artist Toulouse-Lautrec; Jojo, an acrobat at the Circus Fernando, and Sir Henry Collingwood, a mysterious English gynecologist and amateur artist.

Pioneering the as-yet-untried system of fingerprint detection and using cutting edge forensics, including crime scene photography, anthropometry, pathology, and laboratory analysis, Achille attempts to separate the innocent from the guilty. But he must work quickly before the Paris Ripper strikes again.