A French captain (Jean-Pierre Aumont) poses as a Nazi to pinpoint a U-boat base off the coast of France, while assuming the identity of a look-a-like French citizen.
Pierre Metard (Jean Pierre Aumont), a French army captain, working with the British Commandos, is given the assignment to find a secret Nazi submarine base in Brittany. He assumes the identity of a dead French soldier, whom he resembles, since he thinks the base is near the soldier's village. He hopes the villagers will help him and hopes none of them will betray him. He finds a sweetheart, Anne Pinot (Susan Peters) and also a charmer, Elise (Signe Hasso), who, unknown to the villagers,is covertly working with the Nazis. After many narrow escapes , he finds the wall behind which the U-boats are hidden. The commandos make a brilliant raid and destroy the submarine base.—Les Adams <[email protected]>
Free French Captain Pierre Matard (Jean-Pierre Aumont) is assigned the task of locating a concealed U-boat pen in occupied France. He is chosen due to his striking resemblance to Bertrand Corlay, a suspected Nazi collaborator being held prisoner by the British. At the Corlay family farm, Madame Henriette Corlay (Margaret Wycherly), Bertrand's mother, eventually realizes Matard is not her son, but does not give him away, although she disapproves of Bertrand's apparent cooperation with the Germans. Matard has better luck fooling both Anne Pinot (Susan Peters) and Elise (Signe Hasso), Bertrand's fiancee and mistress, respectively. After French Resistance contact Louis Basdevant (Adia Kuznetzoff) is unmasked as a turncoat, Matard forces him at gunpoint to get him into a heavily guarded town. When the masquerade is uncovered, Matard shoots Basdevant and a German officer, and escapes by jumping in the harbor. He sees a U-boat entering a hidden pen. He gives a coded message to Plehec (William Edmunds) to transmit on his wireless, but the man is caught. Matard is also taken. Though a number of civilians refuse to betray Matard (and are subsequently shot), Plehec's young nephew Etienne (Darryl Hickman) identifies him. When Matard refuses to tell Captain Hans Holz (George Coulouris) the location of the wireless, he is tortured for days. Schoolteacher and Resistance member Jean Kerenor (Richard Whorf) and other villagers manage to free him. Hidden in a secret room beneath the church, Matard is nursed back to health by Anne Pinot. Knowing his true identity, she admits she loves him, much to his delight. Etienne shows up, telling Matard that his uncle had instructed him to do whatever he had to in order to protect the wireless. The boy takes Matard to it; Matard sends the location to his superiors. A commando raid is organized, led by Colonel Trane (Reginald Owen). On the way to rendezvous with the British, Matard and Kerenor stumble upon Elise and Holz in each other's arms. Furious that he had defended Elise from the charge of collaboration all this time, Kerenor kills them both. After they depart, Madame Corlay arrives, attracted by the sound of gunfire. When she hears German soldiers approach, she grabs the pistol and allows herself to be captured to shield the others. Matard joins some of the soldiers in the assault on the control room. Becoming trapped inside, they are rescued by Kerenor, who attacks the Germans from behind. Though he is killed, the others succeed in blowing up the sub pens. The commandos re-embark on their boats. Aboard, Matard finds Anne and Etienne.
Immediately upon completing a dangerous spy mission in Northern Africa, Captain Pierre Metard (Jean-Pierre Aumont) is ordered back to the "Free French" headquarters in London. There, Metard learns that his next assignment is to impersonate Bertrand Corlay, a writer and suspected Nazi collaborator whom he greatly resembles. Metard learns many details about the wounded, hospitalized Corlay and even has a replica of Corlay's birthmark imprinted on his back.
Once his education is complete, Metard, whose mission is to discover the exact location of a German submarine base near Corlay's home, parachutes into a field near Corlay's farm and is accosted by two escaped British soldiers. Metard soon convinces the escapees of his loyalties and directs them to Louis Basdevant (Adia Kuznetzoff), his contact in nearby St. Lunaire.
When Metard arrives at the Corlay farm, he is coolly greeted by Corlay's disapproving mother Henrietta (Margaret Wycherly). Metard then reunites with Corlay's fiancée, Anne Pinot (Susan Peters). Although Anne appears happy to see Metard, whom she believes to be Corlay, she tells him that she cannot marry him because of a past infidelity.
Confused, Metard heads for the local inn and discovers that Corlay was having an affair with Elise (Signe Hasso), a seductive Nazi collaborator. Jean Kerenor (Richard Whorf), a disabled schoolteacher, is deeply in love with Elise and accuses Metard, as Corlay, of being pompous and vicious. After Metard agrees to meet the unsuspecting Elise at a ruined castle, Nazi soldiers burst into the Corlay farm, demanding accommodations. When Metard identifies himself as Corlay, however, the commanding officer suddenly changes his mind and departs.
Afterward, Mme. Corlay reveals to Metard that she is aware of his impersonation, but assures him that she will not betray him, as she is ashamed of her son's Nazi affiliations. At the castle, Elise confirms that she is a Nazi collaborator and tells Metard that the submarine base is in St. Lunaire. As Metard is walking back to the Corlay farm, he sees Anne being attacked by a German soldier and kills him. Anne is moved by Metard's bravery and lovingly forgives him. Later, however, Mme. Corlay implores Metard to "go easy" on Anne, and he agrees.
Metard then heads for St. Lunaire, where he meets Louie, a fisherman. After making plans with Louie, who is also helping the English soldiers and a French resistance fighter named Rochet (George Travell), Metard learns that Louie is actually a Nazi collaborator. As feared, Louie betrays Metard, Rochet and the Englishmen to some German soldiers, but Metard manages to overpower the Germans and takes Louie hostage. With his gun jammed into Louie's back, Metard and Louie meet with German Major Von Pless (Lucien Prival), who believes Metard is Louie's cousin. Before Metard can secure safe passage, however, Von Pless discovers his ruse and orders his arrest. Once again, Metard outmaneuvers the enemy and escapes by diving into the bay. While he is swimming to safety, Metard sees a German submarine surface and dock under a hidden sea wall.
Now aware of the base's location, Metard proceeds to Mont. St. Michel, where he relays his findings to Plehec (William Edmunds), a restaurant owner who secretly operates a wireless for the British. Metard then returns to the Corlay farm, unaware that Elise and Capt. Holtz (George Coulouris) suspect him. Although Metard shows Holtz his birthmark, Holtz becomes convinced he is a spy when Plehec's young nephew Etienne (Darryl Hickman) identifies him as the man who visited Plehec.
Metard is taken to jail, where he sees the tortured Plehec killed by the Nazis. Metard is also tortured and starved by Holtz, but like Plehec, refuses to reveal what he knows. With the help of Kerenor, a priest, and other sympathetic villagers, Metard escapes from Holtz's jail and hides in the catacombs of the local church.
There, Anne nurses Metard and confesses that she loves him even though she now knows he is not Corlay. In turn, Metard pledges his love and vows to marry her. To Metard's surprise, Etienne then appears, explaining that his uncle had instructed him to protect the wireless at any cost. Etienne helps Metard out of the church, and Kerenor leads him safely into some woods. After Mme. Corlay bids "her son" goodbye, Metard and Etienne head for the wireless to alert the British.
Kerenor, meanwhile, sees Elise, whose innocence he has always maintained, embracing Holtz in the woods and, enraged, shoots and kills him, then strangles Elise. Hearing the shot, German soldiers rush to the scene, but Mme. Corlay insists that she is Holtz's killer. Metard then relays the submarine base's location, and British commandos launch a sneak attack on St. Lunaire. Overcoming his physical handicap, Kerenor kills many Germans during the ensuing battle, but is himself killed. After British speedboats bomb the hidden base, Metard reunites with Anne on board an England-bound ship and joins her in singing "Les Marseillaise."
