Joseph Cotton plays “Holly,” traveling to postwar Vienna with the intention of reconnecting with an old school friend, "Harry Lime." He learns, however, that his friend died in a car crash. Finding himself without the job he’d been promised, he begins talking with Harry's acquaintances and quickly notices some things don't quite add up, prompting him to investigate further. Getting clear explanations proves increasingly difficult; even those he should be able to trust—like “Maj. Calloway” (Trevor Howard) or "Anna" (Alida Valli), Harry’s lover—seem reluctant or unable to assist. He also starts to feel like someone is watching him, noticing things like the glint of cigarette lights in dark corners and figures lurking in doorways. It begins to dawn on him that his friend might not have been as honest and decent as he'd believed or seemed. From the very beginning, with Anton Karas’s recognizable zither music, we are presented with a richly atmospheric version of Graham Greene's mystery story, and Carol Reed handles the film's rhythm skillfully. The narrative moves forward, but "Holly"—and the audience—have to exert considerable effort, as those involved remain obscured in shadow, which is done very well indeed. It’s an excellent tale concerning trust, faithfulness, and avarice that remains compelling even seven decades later.

Source on TMDB