In a severe winter during World War I, Lieutenant Marechal and Captain Bovardi of the French Air Force became German prisoners in an air battle. Before being escorted to the prisoner camp, they met a man named Feng in a front-line command of the German Air Force. German air force officer in Lao Fen stein. Feng? Lao Fen Stein came from a noble family, dressed neatly and had an arrogant attitude. He found that Bovardi was also a descendant of aristocrats, and there were many acquaintances in social occasions in Paris before the war, and he immediately regarded others with special respect. He is dismissive of Marechal, a former mechanic.

In the German headquarters, the French prisoners were given a friendly reception, because all German officers here hated war, but the good times did not last long. The local police station quickly arrested them and sent them to the prisoner camp.

A group of captured officers from France, Britain, Russia, Belgium and other countries are held in the No.21 Captive Officer Camp. Marechal and Bovardi met several roommates here: Rosenthal, a Jewish capitalist, an engineer, an actor and a teacher. Rosenthal's family has money, and food parcels are often sent. He always shares them generously. The engineer's major is land survey, and his professional knowledge makes him the organizer of the secret plan to dig tunnels and escape. Before Marechal and Bovardi arrived, the tunnel was nearly completed. But just before they were ready to flee, all prisoners of war were ordered to move.

In the new prison camp, Marechal and Bovardi meet Lao Fen Stein unexpectedly. Lao Fen Stein was seriously injured in the air battle and broke his spine, so he had to put on a wire vest, quit the air force and be transferred to the director of the prison camp. Lao Fen Stein welcomed them, but warned them not to plan absconding again.

In the new bunk room, they live with Rosenthal again, and Rosenthal shares the food generously as before. Among the new partners is a bookworm professor and a lascivious locksmith. Just a few days after they settled down, Marechal, Bovardi and Rosenthal began to plan absconding again. They carefully observed the terrain, prepared to weave a rope with sheets, hung a steep wall dozens of meters high from the window, and then fled into Switzerland on foot for more than 3 kilometers.

When the rope is ready, Bovardi puts forward his specific escape plan. He said that he would buy some flutes and distribute them to the whole camp and organize a concert at five o'clock in the afternoon. Five minutes later, the guards will intervene and confiscate all the flutes. At 5: 15, everyone tried to make use of everything that could make a sound, make a scene, and make a big fight. The result must be a gathering of all the people. At this time, he was responsible for the patrol and let them escape. Marechal and Rosenthal were greatly moved by Bovardi's spirit of self-sacrifice.

everything goes according to the predetermined steps. When the prisoners of war were assembled in the yard, the sound of the flute suddenly sounded again. Bovardi was found standing high on the patrol track at the top of the fence, playing the flute. Lao Fen Stein warned him that he must come down immediately or he would shoot. Bovardi tried to stall for time, and Lao Fen Stein shot him. When the guards found Marechal and Rosenthal missing, they had escaped from the prison camp.

Rosenthal twisted his foot in the middle and couldn't travel. Marechal didn't like him at first, so he left him in anger, but he soon came back to help him hide in a farmhouse. The hostess of the farmhouse is a young widow who lives alone with a daughter. She risked her life to protect the two foreigners, giving Rosenthal a chance to recover from his injuries. Elsa said that her husband and brothers all died in the war, and she hated it. In their days of adversity, Marechal and Elsa fell in love. However, the day after Christmas, they were going to set off. Although Marechal and Elsa don't speak the same language, they believe that one day they will reunite in peace.

In the heavy snow, Marechal and Rosenthal successfully crossed the border and regained their freedom.