Pickup on South Street (1953)

On a crowded subway, Skip McCoy picks the purse of Candy. Among his take, although he does not know it at the time, is a piece of top-secret microfilm that was being passed by Candy's consort, a Communist agent. Candy discovers the whereabouts of the film through Moe Williams, a police informer. She attempts to seduce McCoy to recover the film. She fails to get back the film and falls in love with him. The desperate agent exterminates Moe and savagely beats Candy. McCoy, now goaded into action, confronts the agent in a particularly brutal fight in a subway.