Set during World War II, the film follows John Martin and his fellow operative Ellen Rogers as they embark on a perilous mission for the Office of Strategic Services (OSS), the precursor to the CIA. Their task is to infiltrate and sabotage Nazi operations in occupied France. Disguised as civilians, they adopt cover identities and quickly integrate themselves into the local society, all while keeping in contact with their OSS superiors. Tensions run high as they try to blend in and gather intelligence without drawing suspicion. The stakes escalate when they come into contact with skeptical allies and face relentless German officers who will stop at nothing to hunt them down.

As they maneuver through the dangerous landscape, Martin and Rogers develop a deep bond, finding solace in each other while handling immense pressures from their mission. Throughout their time behind enemy lines, trust becomes paramount, not only between them but also with the local resistance fighters who risk everything to aid their efforts. The operatives encounter numerous obstacles and precarious situations that test their courage, resourcefulness, and dedication. With the clock ticking against them, they must navigate treacherous alliances and devise a way to paralyze the Nazi supply routes as initially planned. All these challenges culminate as they become entangled in a life-threatening pursuit, with each decision potentially being their last.