Journalist Étienne Boisset goes to Vidocq's colleague, René Nimier, asking for background to help write Vidocq's biography. Boisset states that he plans to find Vidocq's murderer. Nimier tells him that Lautrennes, Paris' chief of police, asked the pair to investigate the deaths of Belmont and Veraldi, the owners of a cannon factory. Lautrennes believes this is an attempt to undermine the French military in an unstable political climate. Belmont and Veraldi had died in a lightning strike, but during the investigation, Vidocq and Nimier see the powder on a factory worker's clothes catch fire. They interrogate the servant responsible for maintaining Belmont's and Veraldi's suits, who confesses that he received a letter, with cash, ordering him not to clean their jackets. The investigators realize that the lightning would need to be attracted to the men and find metallic pins, decorated with monkey heads, inserted into their hats.