Gilbert, a member of his organization considered by Lupin as a son, incites him to rob the house of the wealthy Dautrecq. But Gilbert actually wants to recover a crystal stopper, just like a third thief, Sebastiani. This one, hollowed out, contains a list of high personalities implicated in a huge financial scandal. Dautrecq uses this list to blackmail them and ensure its power. He also wishes to obtain the favors of Clarisse de Mergy, mother of Gilbert, whom he coveted since his youth. The burglary goes awry when Sebastiani shoots down a servant present on the scene, while being seriously injured himself. The police intervened but Lupin managed to escape. Captured, Gilbert is accused of the murder, Sebastiani having died from his injury. To reveal the truth and save Gilbert from the guillotine, Lupin desperately needs to grab the list. Then engages a duel between him and the terrible Dautrecq, of which he however ends up piercing the secret...
Shots are exchanged between police and criminals, who have just robbed a bank. Commissioner Guerchard is responsible for the case. An obviousness according to him: the blow was committed by Arsène Lupin in person! The prefect of police has a plan: to make believe that the investigation is always carried out by Guerchard, whereas it is entrusted in secret to a large policeman whom Lupin does not know. The man in question is named Victor, from the Brigade Mondaine.
