Jean-Pierre Aumont (billed as "Pierre Aumont") makes his American film debut in this wartime espionage thriller adapted from the blockbuster novel by the famed "Queen of Spy Novels," Helen MacInnes. Aumont plays dual roles: Bertrand Corlay, a Breton farmer with Nazi sympathies, and Pierre Metard, a captain in the Free French Forces. After Corlay ends up in British custody, his astonishing resemblance to Captain Metard is recognized and Pierre is tasked with memorizing another man's life in order to take his place inside Nazi-occupied Britanny. His assignment? Locate and sabotage a secret U-boat pen hidden along the coast. His complications? Corlay's suspicious mother (Margaret Wycherly), Corlay's collaborative mistress (Signe Hasso) and Corlay's beautiful, righteous fiancee (Susan Peters). Turncoats, twists and torture are all in the mix under the assured guidance of director Jack Conway, culminating in a thrilling commando assault on an underground submarine base.