June 1941. Breaching the German-Russian pact, Germany invades the USSR. In the Fresne prison, Claude and Ninette get married. Ninette tells her new husband that, very soon, he will be set free.
Alone in his cell at the Santé prison, Boris writes a letter to Irene. The Kid, also incarcerated, gets a visit from Lili, who is devastated. He implores her to keep fighting.
Lili and André join a group of young resistance fighters, whose leader is FABIEN, a 21-year-old communist, married and father of an infant girl. Along with Cristina, BRUSTLEIN, TOURETTE, TONDELIER, OUZOULIAS, D'ANDURAIN, GAUTHEROT and TITI, they form the Youth Battalions.
In the Lardy Forest, the young crewmembers practice handling grenades, making Molotov cocktails, train sabotage, etc… They debate over whether one should attack any German soldier, even if he's just a grunt?
Back in Paris, the Battalions plan their first action against the Germans. On August 13th, 1941, at the Porte St Martin, about thirty youths get together in the street and unfurl banners against the occupying forces, belting out the French national anthem. The Germans soon turn up and capture Titi and Gautherot, who are shot. To avenge their death, Fabien kills a uniformed German with the help of Brustlein and a third comrade. And André commits his first act of resistance by killing a German sailor. His parents, Mr. and Mrs. Kirchen, know nothing of his clandestine activities. In the Sorbonne chemistry lab, Lili and Cristina blend explosives. Together, members of the Youth Battalions set fire to a building requisitioned by the Germans, and sabotage the Wehrmacht's communication network. Fabien spreads the Resistance to the city of Nantes, where he kills lieutenant-colonel Hotz. The Germans are quick to retaliate by gunning down 48 hostages… including Claude. Ninette is devastated.
Meanwhile, the trial of the Musée de l'Homme network is about to start. Boris attempts to convince the cruel German prosecutor, GOTTLOB, that The Kid is uncompromised – in vain. When Lili visits him, The Kid tells her he will be spared on account of his youth. In the Fresne courthouse, Agnes, Yvonne, Sylvette, The Contessa, Nordmann, Boris and The Kid all stand trial. Weil-Curiel has apparently managed to escape and reach London.
Lili joins Victoria in Lyon, determined to keep up the struggle against the Germans, no matter what. Victoria charges her with the responsibility of reproducing and distributing a new resistance pamphlet entitled Combat. It is being printed in an illegal workshop, by THE PRINTER and his young apprentice VELIN, 21. Lili stays at Victoria's, where she encounters her teenage daughter MIREILLE, as well as two men, BERTIN and MULTON.
At the trial of the Musée de l'Homme network, the accused are being sentenced. The women will either go to prison or be deported to Germany, but Nordmann, Lewitski, The Kid and Boris are all condemned to death. When he hears his sentence, The Kid can't hold back a scream. Irene visits Boris in prison. She is convinced that he will be spared, as his lawyer promised, and so is Boris. At the end of their visit, he hugs her tightly and tells her they will soon be reunited. Once she has gone, he writes her a letter.
Four p.m. at the Mont Valérien. Boris, The Kid, Nordmann and Lewitski are shot dead by the Germans, as Boris' long letter to his wife can be heard in voice-over: "My Love, Darling Irene, forgive me for deceiving you. When I kissed you for the last time, I knew today was the day…"