Based on a novel by Charles Nordhoff and J. N. Hall, escaped convicts on a ship fight for free France rather than go along with the military's capitulation.
A French air force bombs Germany, and on the way back gunner Jean Matrac (Humphrey Bogart) drops a letter to a woman. Reporter Manning (John Loder) is taken to the French air base in England and talks with liaison Captain Freycinet (Claude Rains). At night he sees a farm become an airport. Freycinet tells Manning about Matrac.
Freycinet is on a ship under Major Duval (Sydney Greenstreet). They rescue five men from a canoe, and Matrac says they went twenty days without food. Duval suspects they are convicts from Devil's Island. Renault (Philip Dorn) says they are gold miners from Venezuela. Duval wants them locked up, but Captain Malo (Victor Franken) cancels that order. Freycinet warns Renault, and Matrac admits to Freycinet that they escaped. Renault tells Freycinet their story.
Convicts work making a road in the jungle. Renault says he deserted when he was sixteen. Grandpere (Vladimir Sokoloff) has served his time and sells butterflies, planning escape. The convicts say they would fight for France.
Renault tells how Matrac opposed the Nazis by publishing his opposition to the Munich Pact. Matrac's press is destroyed; he goes off with Paula (Michele Morgan), and they are wed. Paula sees news that Matrac is suspected of murder. She persuades him to flee, but he is arrested on a train and is sentenced to 15 years. Matrac is in solitary and is beaten. Robber Marius (Peter Lorre) contacts Matrac and is keeper of the barracks. Bijou threatens to squeal unless he can go; Matrac says Bijou is in but then knocks him out. They escape and find Grandpere with a canoe. They have to leave one behind, and Petit (George Tobias) is worried because he is the heaviest; but Grandpere says he is staying. Grandpere makes them promise to fight for France.
On the ship Freycinet says he will help them. Captain Malo announces Petain's capitulation, but he tells Freycinet he is taking the cargo to England without telling Duval. Matrac asks Freycinet to let him off before they get to Marseilles because he does not trust Duval and wants to return to his wife. Major Duval takes over the ship to go to Marseilles under German discipline. A boy shouts, "Vive la France!" and a fight breaks out. Matrac and Marius gain control of the machine guns. Captain Malo resumes command. Jourdain radios their position until Petit stops him with a club. A German plane attacks the ship, causing fires. Matrac shoots the plane down, and Marius dies. Matrac shoots the survivors on the plane.
Freycinet tells Manning they made it to England. Planes return. Paula celebrates her son's birthday, but Matrac's plane can't fly over. The plane makes it back to England, but Matrac was killed. At his funeral Freycinet reads Matrac's letter to his son that hopes for healing after the war.
This war propaganda implies that even though the French
are captives of the Germans, some of them are still fighting on
the English side.