Philippe Gerbier, Lino Ventura, the head of a French Resistance cell, is arrested by Vichy police on suspicion of Resistance activity. Although he is acquitted due to a lack of evidence, he is still sent to an internment camp. He and a young Communist work on an escape plan, but before they can execute it, Gerbier is transported to Paris. While waiting to be questioned by the Gestapo, he manages to kill a guard and flee.
In Marseille, Gerbier, Félix Lepercq [Paul Crauchet], Guillaume ‘Le Bison’ Vermersch [Christian Barbier], and Claude ‘Le Masque’ Ullmann [Claude Mann] trick Paul Dounat, the young agent who betrayed Gerbier, [Alain Libolt] into meeting them. They take him to a house, but discover the neighboring house is newly occupied, so they cannot use their guns to kill Dounat. Lacking a decent knife, they strangle their former associate.
Félix meets his old friend Jean-François Jardie [Jean-Pierre Cassel] in a bar and recruits the risk-loving former pilot to join the Resistance. While on a mission to Paris, Jean-François visits his older brother Luc Jardie [Paul Meurisse], a renowned philosopher who appears to live a detached, scholarly life. He then travels to the Mediterranean coast to help evacuate some Allied soldiers, along with Gerbier and the ‘Big Boss’, to London via a submarine to Gibraltar. Jean-François does not recognize him in the dark, but the Big Boss turns out to be Luc, whose identity is a closely guarded secret.
In London, Gerbier tries to arrange additional support for the Resistance from the Free French leadership, and Luc is decorated by Charles de Gaulle. When Gerbier learns Félix has been arrested by the Gestapo, he cuts his trip short and parachutes into the French countryside.
After Félix’s arrest, Mathilde [Simone Signoret], a Parisian housewife who is part of the Resistance, moves down to Lyon to run Gerbier’s cell. Gerbier is impressed by her abilities, so he keeps her around. She devises a plan to rescue Félix, who is being tortured at the Gestapo headquarters. Jean-François, after hearing the details, writes Gerbier a letter of resignation and incriminates himself with an anonymous letter to the Gestapo so he will be jailed with Félix. Mathilde, Le Masque, and Le Bison try to rescue Félix disguised as Germans and with a forged order to transfer him to Paris, but their plan fails when the prison doctor pronounces him unfit for transport, as he is barely alive. When Jean-François, who has also been badly beaten, sees the rescue has failed, he gives Félix his only cyanide pill.
Having seen Gerbier’s picture on a wanted poster during the rescue attempt, Mathilde urges him to lie low, but he says there is no one who can take his place at the moment. He is swept up in a raid by Vichy police and handed over to the Germans.
Taken to be executed, Gerbier and his cellmates are told that, if they can reach the far wall of a room before they are killed by machine gunners, they will be allowed to live a little longer. Once the shooting starts Gerbier runs to the wall, when suddenly Mathilde and Le Bison appear by a window and throw smoke bombs to block the Germans’ view and a rope to help Gerbier. He climbs it and escapes with the group.
Gerbier goes to hide out for a month in an abandoned farmhouse. One day, Luc arrives to discuss what to do about Mathilde, who has been arrested. He worries she will inform on her confederates, as her teenage daughter has been threatened. Luc hides when Le Masque and Le Bison arrive with the news that Mathilde is free and two members of the Resistance have been captured. Gerbier orders Mathilde’s immediate execution, but Le Bison refuses to do so and swears to prevent Gerbier from killing her, so Luc emerges and convinces Le Bison that Mathilde would want them to kill her before she is forced to identify anyone else.
Luc accompanies Gerbier, Le Bison, and Le Masque to Paris. They locate Mathilde on the street, and Le Bison shoots her twice before they drive away. Closing text reveals that all four men were captured and died within less than a year, either through suicide or at the hands of the Nazis. Gerbier’s precise fate is succinctly described as “on 13 February 1944, he decided not to run this time.”
