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.

In France during World War I, Marthe waits for her husband, Jacques, while he fights on the front lines. Marthe then begins a tempestuous affair with 17-year-old François, with whom she had a dalliance before marrying Jacques. Jealous François struggles with the fact that Marthe is married, while she tries to prove her devotion to her young, hotheaded lover. Things become even more complex when Marthe becomes pregnant with Jacques' baby.

Léontine, an old baroness, opposes her granddaughter's wedding for moral reasons. But Adolphe, her first husband reminds her that her own conduct in the past was far from irreproachable. Didn't she cheat on him ? And after her divorce from him and her remarriage with a baron, didn't she do the same thing to her second husband? Léontine then realizes she is in no position to lecture her granddaughter, all the more as she loves her fiancé truly.

Hopson, a prestigious scientist, studies the effect of snake venom to cure many diseases of mankind. His son enlists in the army when the Great War breaks out. A series of circumstances will lead the scientist to change his way of thinking about values ​​and principles that until then he had as immovable.

With Jean-Baptiste at the front, Louise takes care of Bébé with the help of Uncle Pierre. The letters she receives from Jean-Baptiste worry her, but Pierre distracts Bébé with a box of tin soldiers. That night, Bébé has a dream of his soldiers vanquishing the enemy, and the next morning, Jean-Baptiste surprises the family by returning home.