Heroes of the Marne (1938)

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.