Bernard Lefrancois is a prosperous farmer on the River Marne, while his neighbor is impoverished. Lefrancois objects strongly to the romance between his son and the neighbor's daughter, but it continues in secret. WWI begins and the son becomes an aviator with the French army, and the unwed girl presents Lefrancois with an unexpected grandchild. The German army occupies the area, and the girl is serving France as a spy and securing information needed by the French to drive out the Germans. While his son is engaged in air-combat against the Germans, and the unwed mother of his grandchild is serving as a spy against their country's enemy, Lefrancois also joins the battle as a soldier.

The gratuitous murder of his father and the misery of the people, aggravated by a succession of bad harvests, lead Gaspard, a great admirer of Mandrin and blacksmith by profession, to revolt. With his companion Samplan, he finds himself at the head of a handful of soldiers dissatisfied with their fate and a band of brigands. They steal money from the rich to give it to the poor, like highwaymen, vindicators with a big heart. In their eyes, things cannot go on like this, in this country which seems given over to the decadence of the nobility and the whims of an indolent king. Gaspard and his troupe are responsible for making it known.