Odette Sansom, a mother of three, answers a radio request for photographs of France and writes to the Admiralty, but a misaddressed letter brings her to the attention of the Special Operations Executive, which seeks French volunteers to return to their homeland as espionage agents. After completing training in September 1942, she is sent back to France, ready to play a dangerous part in the resistance.
She travels to Cannes, where she is met by Captain Peter Churchill, her superior, and she also meets Arnaud (Adolphe Rabinovitch), another agent. Her first assignment is to journey to Marseilles to obtain plans for the docks there, a mission that tests her nerve and stealth under the pressure of war. The team is barely warned of a raid organized by Abwehr Colonel Henri, and Odette, Peter, and Arnaud must relocate to Annecy, where they rendezvous with Jacques to regroup and plan further actions.
Seeing the growing strength of the local resistance, Peter pushes for arms, medicines, and other support for the Maquis, while he himself is recalled to London. A large airdrop of supplies is arranged to keep the network alive in the field. Yet the danger closes in. Colonel Henri tracks Odette to Annecy; from a captured agent he learns the extent of Odette’s network and asserts that he and others disillusioned with Hitler want to make contact with the British. Odette suspects a trap and orders the other agents to disperse, trying to protect the circle she has built.
Not long after Peter returns to France, Odette and Peter are captured in Annecy by Henri and are taken to Fresnes Prison, with Arnaud away when the hotel raid took place. Odette endures brutal interrogation by the Gestapo but refuses to break, and she is sentenced to death. An apologetic Henri visits her, and at her request he arranges for one last glimpse of Peter, though she conceals her fate from him.
From there she is transported to Ravensbrück concentration camp, where she is placed in solitary confinement. The Germans convince themselves that Odette fabricated Peter’s role, portraying him as a dashing but frivolous figure while she is the mastermind behind the operation; in reality, Peter remains a prisoner, left to endure the consequences of their work. As the war shifts in the Allies’ favor, the camp commandant’s orders shift as well: on 16 April 1945, with Germany in collapse, he orders the execution of prisoners but ultimately chooses to spare Odette, directing a subordinate to safeguard her. When news of Hitler’s death reaches the inmates, riots erupt. A guard comes for Odette, and she fears execution, but the commandant instead ferries her to the advancing American forces, believing she is Peter’s wife and thus connected to the British Prime Minister.
Back in England, Odette is finally reunited with [Captain Peter Churchill], and the two confront the years of danger, sacrifice, and deception that marked their shared mission. The film closes with a title card reflecting on Odette’s fate and the enduring impact of her courage and resilience in the face of oppression.
