While in a POW camp, a man discovers his best friend was his wife's lover.

A prisoner in a World War I German prison camp for Allied soldiers starts a riot when he commits suicide. For punishment, all the men are confined to a cramped dungeon. Fred Allison, a captured British officer, begs fellow Oxford graduate Carl Erlich, the commandant of the camp, for the men's release, promising to be personally responsible for their behavior. Among a new batch of prisoners is Jack Digby, an old friend of Allison. Since Digby had seen Allison's wife Monica shortly before his capture, Allison questions him about her. He doesn't know that Digby and Monica have fallen in love, and Digby feels guilty about betraying his friend. Digby plans to escape although Allison begs him not to try because of the trouble it will cause for the other men. Digby ignores his pleas and escapes in a nearby plane the same night another soldier rapes and murders a young German woman. Believing Digby to be guilty of the crime, the Germans request his return. Erlich asks Allison to sign the request, and he initially refuses, but when he sees a letter from Monica to Digby in which she declares her love for him, he changes his mind and signs the request. At his trial, Digby accuses Allison of condemning him to death for having an affair with his wife. After Digby is sentenced to be shot, Allison finds a confession in his room from the guilty soldier, who has since committed suicide. Allison allows the execution to proceed until the last minute, when he reveals the real murderer and frees Digby. Allison then tells Digby that he has planned an escape for the entire camp. He mans a large gun, keeping the Germans at bay while the rest of the men escape in German planes. Digby returns to rescue Allison, but he is too late--Allison is dead. Erlich and Digby salute his corpse.