At the end of the 19th century, during a ball in Joinville, on the outskirts of Paris, Georges, a former delinquent working as a carpenter, meets Marie, a young woman connected to a criminal gang.
Paris, France. Commissaire Wens is put in charge of the investigation into the murder of one of six friends who, in the past, made a very profitable promise.
The local building-contractor Martin Roumagnac is fascinated by the fashionable Blanche Ferrand. To impress Blache, Martin presents her with a villa. However, this ruins him financially. Despite Martin's many efforts for the now femme-fatal Blanche, she is not able to chose between him and the rich consul De Laubry.
A mysterious figure signing himself "The Ferret" keeps sending letters to the police, tipping them off about murders that are to be committed around Paris. Among those caught up in the police manhunt is a fraudulent clairvoyant.
Adrien Moulinet, a modest encashing agent in the Nortier bank, is also an inventor in his spare time. His latest revolutionary creation is the motorized roller skate. His problem is to be able to market them. Jules Petitpas, a jobless adman, is the right man for that.
