Based on a true story, two French officers escape from a German prison camp.
In 1916 French pilot Lt. Maréchal (Jean Gabin) is sent to take photos; but he is captured with Captain de Boieldieu (Pierre Fresnay) by Captain von Rauffenstein (Erich von Stroheim) and invited to dinner. Maréchal and de Boieldieu are put in a prison camp for officers and told they must obey the Germans. Packages sent for Lt. Rosenthal (Marcel Dalio) from his Jewish banking family provide good food. The French are digging a hole to escape. Cartier (Julien Carette) digs in the tunnel, while the German Arthur (Werner Florian) tells of a prisoner who was shot trying to escape. As they garden, men drop dirt. Rosenthal's crates include dresses. In a talent show Cartier sings, and others in dresses dance. Maréchal announces a city was recaptured, and they sing "The Marseillaise." Maréchal tries to escape and is brought back to solitary, where a guard gives him a harmonica. Maréchal returns to his comrades, but they are transferred to another camp, and the British don't understand his telling them about the tunnel.
Rauffenstein remembers de Boieldieu and commends him and Maréchal for their many escape attempts. Rauffenstein uses French regulations and gives them the book. He shows them his medieval castle, and they are put with Rosenthal. They make and hide a rope. Rauffenstein accepts de Boieldieu's word, because he is an aristocrat, lamenting he is only a policeman now because of his wounds. Maréchal tells Rosenthal that he is more of a pal than de Boieldieu. Books arrive from the Czarina, but the Russians burn them. De Boieldieu tells Maréchal and Rosenthal to escape when he distracts the guards. Men play flutes, which are taken away by guards. Then they hit pans and are ordered to roll-call; but de Boieldieu is absent, playing a flute. As guards search, Rosenthal and Maréchal go down the rope and escape. Rauffenstein warns fleeing de Boieldieu to come back. When de Boieldieu goes on, he shoots him. Rauffenstein calls out dogs to find Maréchal and Rosenthal. Rauffenstein asks dying de Boieldieu to forgive him.
In winter cold Maréchal and Rosenthal walk and sleep; but Rosenthal's sprained foot gets worse. They are out of food and quarrel; Maréchal leaves but comes back for Rosenthal. They go to a farmhouse, where Else (Dita Parlo) takes them in and gives them food. German soldiers march by. Else says her husband was killed at Verdun. They celebrate Christmas with her little girl. They say good-night, and she kisses Maréchal. Rosenthal tells Else that they are going. She tells Maréchal that he made her happy, and he promises to return after the war. In the snow Maréchal and Rosenthal make it to Switzerland.
Nazi propagandist Goebbels considered this film cinematic enemy number one. With little violence it shows humans on both sides caught in the captivity of a war that will destroy European aristocrats' supremacy.