Harry Palmer (Michael Caine), a former British spy, stumbles into a complex plot to overthrow Communism using a sophisticated computer system known as "the billion-dollar brain." As he navigates a web of intrigue involving anti-communist organization leader General Midwinter and his loyalist agents, Harry must use his skills to uncover the truth behind the conspiracy. With the help of Leo Newbigen (Karl Malden), Harry's old friend and handler, and Anya (Françoise Dorléac), a woman with her own agenda, he embarks on a thrilling adventure that takes him from Helsinki to Texas, where the fate of the world hangs in the balance.