Plot
During World War II, Vincent Van Der Lyn, a former schoolteacher who became a Dutch resistance fighter, causes so much trouble for the Nazis that they place a bounty on his head. As a result, he is ordered by his superiors to travel to England via neutral Lisbon.
On Van Der Lyn's arrival in Lisbon, Police Captain Pereira notes that his passport has no exit stamp on it, indicating that he sneaked across the border, however reassures Van Der Lyn that as long as his Portugese visa is in order there is no issue. German agent Otto Lutzke becomes suspicious, informs his superiors and starts tailing Van Der Lyn.
At a restaurant, Van Der Lyn is pleasantly surprised when a beautiful French woman, Irene Von Mohr, sits down at his table. Moments before, Irene had passed a card to a man in a nearby alley, only to witness him being shot in the back by an unknown assailant soon after. She flees into the restaurant, but as the police arrive to search the place, she quickly sits down at Van Der Lyn's table to throw off suspicion. She identifies herself to Van Der Lyn as merely a frequent gambler at the Casino Estoril. She excuses herself, supposedly to make a telephone call, but never returns. Van Der Lyn goes to the aforementioned casino where he finds Irene. As she warns him to stay away from her, they are joined by senior German diplomat Hugo Von Mohr and Lutzke. The Germans soon identify Van Der Lyn as the saboteur known as the "Flying Dutchman."
Van Der Lyn meets the local resistance leader, Ricardo Quintanilla, who introduces him to other members of his resistance group: Pole Jan Bernazsky, Norwegian Anton Wynat, and Frenchman Paulo Leiris. Quintanilla asks Van Der Lyn to brief Jennings, Van Der Lyn's replacement. In private, Quintanilla warns Van Der Lyn that he suspects one of their group is a traitor.
The next day, when Irene gets into her automobile, Van Der Lyn invites himself along for the ride. At first annoyed, she gradually warms to him, and they spend the day together. He professes that he is in love with her. She reveals that she is married to Hugo, who rescued her from Dachau concentration camp.
When Van Der Lyn returns to his hotel room, he finds Jennings slumped over his desk. Before he dies, Jennings is able relay a message that his killers have taken "the eagle". Acting on a false tip, the police arrest Van Der Lyn for Jennings' murder. A distraught Irene informs Captain Pereira that she was with Van Der Lyn the entire day, but declines to testify against him in court. When she visits Van Der Lyn in jail, he angrily accuses her of framing him.
Van Der Lyn escapes from jail after attacking a guard. Irene finds him and offers to take him to Quintanilla, revealing that she is a resistance fighter as well. His suspicions towards Irene are softened after she gives him a gun. When they reach Quintanilla and the others, they charge him with being a traitor. Van Der Lyn himself concedes that they would be foolish not to kill him. However, when he mentions Jennings' dying message to Quintanilla, they know he must be telling the truth, as "the eagle" was a rare coin that was to have been used to identify Jennings. Hugo is then revealed to be a double agent working with the resistance.
Quintanilla decides to set a trap by informing the group that Jennings' replacement is in the casino hotel, since he knows that the Germans will move to eliminate him to plant their own agent. Pereira spots Van Der Lyn, but is persuaded to trust him and wait a few minutes for the real murderer to be revealed. Quintanilla informs the group that the new agent's room number is 865, and that they will meet him in fifteen minutes. Shortly after, the group gathers at a roulette table along with known Nazi agents. Hugo places bets on 8, 6, and 5, revealing that he is the traitor. Quintanilla and the others escort him away, but he manages to escape and flee the casino. Hugo is pursued by Van Der Lyn and Captain Pereira, who kill him in a shootout. Van Der Lyn finds the eagle coin in one of Hugo's pockets.
Van Der Lyn departs Lisbon on a boat to return to occupied Europe in Jennings' place. Irene promises to wait to learn of his safe passage across the border, and Vincent promises to come back to her.
