British Captain Terence Stevenson, Robert Donat, is drawn into a danger far beyond his routine bomb disposal work. Fluent in Romanian and German and trained in chemical engineering, he parachutes into occupied Europe to assume the identity of Captain Jan Tartu, a covert operative tied to the Iron Guard, with a dual objective: seize the formula for a new Nazi poison gas and sabotage the plant that manufactures it.
His mission runs into a snag when his contact is arrested before any job can be secured. Undeterred, Tartu is reassigned to the munitions side of the operation, working as a foreman and donning a German uniform. He is billeted at the house of Anna Palacek, Phyllis Morris, where he lives alongside German Inspector Otto Vogel, Walter Rilla, and the captivating Maruschuka Lanova, Valerie Hobson. Maruschuka’s charm helps her keep pace with the German officers, while Pavla, Anna’s daughter, quietly watches and waits for the right moment to act. The tension of loyalty and betrayal hangs heavy as Tartu carefully navigates the delicate balance of his cover and his true allegiance.
The turning point comes when Pavla shoots a German who had ordered the execution of her lover. Tartu steps in with an alibi, earning Pavla’s fragile trust, and then reveals his secret identity as a spy. With trust reluctantly earned, he seeks the underground’s help to reach the chemical plant. To his surprise, Pavla arranges a date that brings him together with Maruschuka, a moment that hints at a fragile alliance between two people who are both suspicious of the Nazi regime—and perhaps more sympathetic to the resistance than they admit.
At work the next day, Pavla’s sabotage attempt is noticed. She whispers to Tartu to protect himself by denouncing her, a dangerous move that backfires when she is executed in a stark display of Nazi ruthlessness. The factory manager, impressed by Tartu’s apparent loyalty, grants him the transfer he desires—the transfer that will place him inside the very heart of the plant he came to destroy.
Meanwhile, Maruschuka reaches out to Dr. Novotny, the head of the local resistance group, Martin Miller, signaling her trust in Tartu. Yet the resistance already suspects him and schemes to safeguard their own interests, even if it means signaling Vogel to act. Maruschuka, determined to keep her own plans alive, flirts with Vogel in a bid to uncover Tartu’s true loyalties, hoping to force a confrontation that might reveal the truth.
Under pressure, Tartu moves to work for Dr. Willendorf, Percy Walsh, the head of the chemical plant. He learns that the first shipment of gas is scheduled for the upcoming night, heightening the clock’s tick. Desperation fuels a risky gambit: Tartu pretends to drink himself into reckless bravado in a bar, bragging about six Czech resistance members who are about to be rounded up. His bravado is overheard by the underground, who abduct him and, after a tense night, come to the realization that they share a common purpose. Working through the night, they manufacture a set of miniature bombs designed to devastate the plant when placed correctly.
Back at the Palacek house, Vogel is on the scent and checks Tartu’s credentials, reporting the spy theory to Maruschuka. Believing the information, she confronts Vogel and, in a pivotal moment, accidentally kills him. Gripped by the need to protect herself and the mission, she hurries to the chemical plant to warn Tartu. He triggers an air-raid alarm and moves through the plant, placing the bombs with meticulous care as the German guards tighten their perimeter. The explosions erupt with devastating force, the plant reduced to ruin, and Tartu narrowly escapes with Maruschuka and a getaway pilot.
In the final breath of peril and hope, the group slips away aboard a stolen German bomber, breaking free from pursuit and finding a precarious moment of safety. As the engines roar into the distance, a quiet, defiant bond forms between Tartu and Maruschuka, and he voices a simple, almost intimate wish for the future a little away from the war: > "just a simple little wedding."
