During World War I, two French airmen are shot down while taking surveillance photographs over German territory. Captain De Boeldieu, a wealthy aristocrat, and Lieutenant Marechal, a mechanic in civilian life, are captured and send to a POW-camp where they meet Rosenthal, son of rich Jewish bankers. After their first attempt to escape has failed they are send to an old castle-turned-POW-camp. The camp is under the command of wounded war veteran von Rauffenstein, a former air force officer. Von Rauffenstein takes an immediate liking to de Boeldieu, as they are members of the same social class and convinced believe that their political ideals will soon be a thing of the past. The Frenchman discover that their fellow-prisoners have long been digging an escape tunnel and they all agree to help. But while Maréchal and Rosenthal join in with enthusiasm, de Boeldieu does so out of a sense of duty. When de Boeldieu stages an escape attempt in order to divert the attention of the guards away from his escaping comrades he is shot by von Rauffenstein. Maréchal and Rosenthal manage escape, they find refugee in the home of a German war-widow and finally reach the Suiss border.