Juan Pujol Garcia, a Spanish double agent codenamed Garbo, sends the Germans a stream of fabricated reports in the months before June 1944, convincing Hitler's intelligence service that the real invasion will land at Calais rather than Normandy. This film follows Garbo and the wider network of agents and resistance fighters who fed false and genuine intelligence across the Channel, using archival footage, surviving documents, and expert testimony to reconstruct how the deception was built and maintained under constant risk of exposure. It traces how ordinary men and women, recruited into espionage work, transmitted radio messages from occupied territory, ran double-agent operations, and helped convince the German high command to hold reserves away from the actual landing beaches. The film also weighs the personal cost of that work: the strain of maintaining a false identity for years, and the danger faced by anyone caught relaying information to London. Garbo's deception is treated as the clearest case of espionage directly shaping the outcome of the invasion.