Portrait of a two-faced man. By day he is rich, brilliant and respectable financial officer Lussac; at night, he becomes "Mirror", a ruthless gang leader in Marseilles.
Taking advantage of their uncle's absence, André and Raymond Rafet organize a New Year's Eve party at his house. The uncle returns unexpectedly, disturbs the party, threatens his nephews to disinherit them and then locks himself in his office. A few minutes later, he is found dead, poisoned.
Pierre can no longer pay for his medical studies and disappears for several months. During his absence, his fiancée allows herself to be courted by a reveler. Back home, Pierre cannot regain the trust of the young woman, who now leads a dissolute life of which she is ashamed. She tries to kill herself. Pierre saves her and heals her.
