The Third Man (1949)

Set in a bombed-out, post-war Vienna, THE THIRD MAN stars Cotten as Holly Martins, a writer of pulp Westerns, who arrives penniless as guest of his childhood chum Harry Lime, only to find him dead. Martins develops the ultimate conspiracy theory after learning of a "third man" present at the time of Harry's death, running into interference from investigating British officer Trevor Howard and falling head-over-heels for Harry's grief-stricken lover, Alida Valli.