André Laroche, an industrialist, has just passed away. Face to his grave, as he is being buried, Anne de Vierne, the wife of a magistrate, confesses to her son François that Laroche was in fact Lupin and that he is his natural child. But he is not the gentleman thief's only offspring! Lupin had indeed another son by a housemaid, Gérard Dagmar, a dancer, magician and - occasionally - burglar. Which complicates the task of François who, to respect the last wishes of the testator, has gone in search of the treasure of Poldavia. For he keeps finding Gérard on his way and his efforts are constantly thwarted by his half-brother. Will Gérard prevent François from becoming the worthy successor to their father or will the two young men decide to join forces? That is the question.
Jean-Pierre Cassel
as Gérard Dagmar
Jean-Claude Brialy
as François de Vierne
Françoise Dorléac
as Nathalie
Geneviève Grad
as Catherine
Jean Le Poulain
as Le préfet de police
Michel Vitold
as Baron von Krantz
Anne Vernon
as Madame Bellac
Daniel Cauchy
as Charly
Henri Garcin
as Hans
Yvonne Clech
as Madame de Vierne
Fernand Fabre
as M. de Vierne
André Badin
as Le chroniqueur mondain débutant
