In postwar Vienna, Austria, Holly Martins, a writer of pulp Westerns, arrives penniless as a guest of his childhood chum Harry Lime, only to learn he has died. Martins develops a conspiracy theory after learning of a "third man" present at the time of Harry's death, running into interference from British officer Major Calloway, and falling head-over-heels for Harry's grief-stricken lover, Anna.

Jeff Bailey seems to be a mundane gas station owner in remote Bridgeport, California. He is dating local girl Ann Miller and lives a quiet life. But Jeff has a secret past, and when a mysterious stranger arrives in town, Jeff is forced to return to the dark world he had tried to escape.