Prosecutor Etzel discovers that his father has sentenced a man, Leonardo Maurizius, on mere presumptions. He then makes it a point of honor to trace the sources of the case to uncover the truth.

The title of this French "reality" drama, which translates to Before the Deluge, is a play on Louis XVI's famous prognostication, "Apres moi, le deluge." Set in 1950, the film concentrates on five Parisian adolescents. Certain that the next war will herald the apocalypse, the youngster make plans to run off to a desert island and set up a new society. This, however, will require money, which is why the boys decide to pull off a "necessary" robbery. Idealism collapses in the face of cold reality, as the five youths suffer from the consequences of their actions. Avant le Deluge was one of a group of films cowritten by director Andre Cayatte and Charles Spaak which endeavored to explore the touchy social issues of the day: others in the Cayatte-Spaak canon include the euthanasia-themed Justice est Faite and the capital-punishment tract Nous sommes tous des assassins.

Stefan Borba was a member of a spy ring during the war but after the end of the conflict he opted out. Now he is a miner in Belgium and lives happily there with his wife Denise. Unfortunately for him, his past catches up with him. One day indeed, Milan, a secret agent with whom he used to work, resurfaces and forces him back into action...

Guillaume Dodut is a stationmaster in rural France at a station where trains no longer stop. His dream has always been to holiday in the famous resort town of Biarritz. Meanwhile, he gets involved in the romantic life of his son who is studying to be an engineer in London.

In 1944, in a small village in Calvados, just as the Allies landed, a British plane was shot down. The wounded pilot seeks help. All the villagers, who speak only of resistance, refuse to help, for fear of reprisals. Only the mayor, Dr. Leproux, takes him in and nurses him back to health, then entrusts him to the Resistance. But the Germans get wind of the story and arrest Leproux. He is saved by Major Frantz. But the budding friendship between these two men "doesn't stop the drums", and the war is on.

In Romagna, an Italian district, at the beginning of the twentieth century, the owners of an estate are the professor Edoardo, always lost in reveries, and his wife Maria. They have a son, Robertino, who has a friend: Zvanin. Zvanin is the son of Mingòn and Marianna, two peasants. Dolly is an american cousin and every summer she comes in Romagna. The movie narrates their stories over the years until the post I World War period.