In post-World War II Vienna, divided into international zones by the Allied powers, American Holly Martins arrives to meet his old friend Harry Lime, who has offered him a job. Upon his arrival, Martins learns that Lime has been killed in a traffic accident. While attending Lime's funeral, Martins meets two of Lime's friends, a British officer named Major Calloway and Lime's girlfriend, Anna Schmidt. Despite Major Calloway's claims that Lime was a criminal involved in racketeering and other unsavory activities, Martins is skeptical and begins his own investigation into Lime's death. His inquiries lead him to question the inconsistencies in the accounts of Lime's demise.

Persistent in uncovering the truth, Martins delves into the seedy underworld of a city struggling to rebuild from the war's destruction. He becomes increasingly entangled in the complex web of lies and half-truths surrounding Lime's life and death, as he tries to clear his friend's name. Martins meets with various acquaintances of Lime and retraces the events leading up to the accident. As he does so, he faces moral dilemmas and his friendship with Lime is tested. Meanwhile, his growing attraction to Anna complicates his quest, as she harbors her own personal grief and secrets related to Lime's past. Martins' search for clarity reveals a dark and treacherous postwar Vienna, where nothing is quite as it seems.