Pickup on South Street (1953)

On a New York subway, FBI agents are shadowing Candy (Jean Peters), a femme fatale who is delivering stolen government microfilm to her communist boyfriend. Pickpocket Skip McCoy (Richard Widmark) unwittingly filches the film and is out the door before the G-men realize what happened. Both the feds and the reds give chase as McCoy catches up with Candy and romances her at his dockside shack. Streetwise snitch Thelma Ritter, who is helping the cops locate McCoy, earned an Oscar nod for her supporting role.