Vidocq and Annette return to Paris, where they plan to hide out with Gibassier, Vidocq's former comrade and blackmailer. But when they arrive, Gibassier is dead and Vidocq is arrested for his murder. He escapes and returns several times to M. Henry, chief of the Paris police, to obtain permission to find the real culprit himself. Disguised as Gibassier, he waits for the murderer to return to finish the job...

It's only been a few months since Vidocq began working for the police, complaints from jealous officers are multiplying and Mr. Henry is ready to dispense with his services. One last chance comes up for Vidocq: the police museum has been broken into, and the Emperor's hat and the black diamond have disappeared. Vidocq has just a few days to find these objects before the Emperor himself inaugurates the museum...