Arsène Lupin decides to run a detective agency in addition to being a gentleman thief. As a detective he happens to cooperate with police in order to unveil the criminal activities of a villain. When he succeeds the villain returns the favour. The unmasked Arsène Lupin manages to escape with the villain's gangster moll as his new companion.
Jules Berry
as Barnett, alias Arsène Lupin
Gabriel Signoret
as L'inspecteur Béchoux
Suzy Prim
as Olga Vauban
Rosine Deréan
as Germaine Laurent
Aimé Simon-Girard
as Le journaliste
Thomy Bourdelle
as Cassire
Mady Berry
as Victoire
Abel Jacquin
as Brémond
