O.S.S.

John Martin attempts to steal plans from a Baltimore plant and is arrested for espionage. He is turned over to the Office of Strategic Services, which recruits and trains new operatives by sending them on test missions. This marks the start of his covert career.

Martin teams with Gates, Parker, Bernay, and Elaine Dupree to travel to France. They operate under assumed names and aim to blow up a railroad tunnel to disrupt Axis troop movements ahead of the Allied invasion. The mission sets the stakes high for their entire operation.

During their first assignment in rural France, German agents attack the group and kill Gates. The ambush exposes the constant danger the OSS team faces behind enemy lines. The loss raises the urgency of completing their mission.

Colonel Paul Meister interrupts the maquis gathering and becomes infatuated with Elaine. Elaine crafts a bust of Meister and, after he leaves for Normandy, she and Martin assemble a duplicate bust packed with plastique explosive. They trigger the tunnel blast, and Martin returns under fire to rescue Elaine, who then insists he never jeopardize a mission for her again.

On foot, the team meets Bernay, their radio contact with the OSS. He helps coordinate operations as the mission progresses through occupied France. The group relies on him to relay critical information to OSS command.

Amadeus Brink, a Gestapo officer, helps secure their safety and a fortune by manipulating the mission. He removes Martin and Elaine's ‘wanted’ file from the Gestapo and arranges for a cousin to deliver a diplomatic pouch for photocopying. Bernay hides the negative in the lining of Martin's hat to preserve evidence.

Against Brink's advice, Bernay radios that the Nazis have broken one OSS secret code. He is gunned down, and Martin and Elaine are briefly questioned by the Gestapo, but released before Meister catches Brink with their papers.

With safety in sight, Martin and Elaine must contact Parker, an OSS agent near the Rhine, and rely on him to identify the agent who will recognize them. They go to a farmhouse where Elaine is confronted by drunken German soldiers. Parker supplies the troop dispositions, while Martin goes to radio the information; Meister arrests Elaine while he is away.

While Martin is away gathering positions, Colonel Meister arrests Elaine, threatening the completion of the final mission. The arrest creates a tense standoff as the Allied advance presses on. The outcome of the mission hangs in the balance.

As American troops advance through France, Brady reveals that Elaine's real name was Ellen Rogers. The revelation shifts the story toward personal reflection and questions about loyalty and identity. Martin contemplates the possibility that she may have been the girl next door in his hometown.

The summary closes with the Allies pushing through France and Martin's contemplation of Elaine's past, hinting at unresolved emotions and the vagaries of undercover life. The film leaves their relationship and future uncertain as the war continues unabated.