The Third Man is a 1949 British FILM NOlR directed by Carol Reed, written by Graham Greene, and starring Joseph Cotten, Alida Valli, Orson Welles, and Trevor Howard. Set in postwar Vienna, the film centres on American Holly Martins (Cotten), who arrives in the city to accept a job with his friend Harry Lime (Welles), only to learn that Lime has died. Viewing his death as suspicious, Martins elects to stay in Vienna and investigate the matter.
In 1999, the British Film Institute voted The Third Man the greatest British film of all time. In 2011 a poll of 150 actors, directors, writers, producers and critics for Time Out magazine saw it ranked the second best British film ever.
You can find out more about this movie from Wikipedia.