After being captured and held in a German prison camp during World War I, a group of French soldiers, including the patrician Captain de Boeldieu and the working-class Lieutenant Maréchal, grapple with their own class differences. When the men are transferred to a high-security fortress, they must devise a plan to escape under the watchful eye of aristocratic German officer von Rauffenstein, who has formed an unexpected bond with de Boeldieu.