On a crowded New York City subway train, pickpocket Skip McCoy (Richard Widmark) steals Candy's (Jean Peters) wallet. Unbeknownst to Skip or Candy, in the wallet is microfilm of top-secret government information. Candy was delivering an envelope as a final favor to her ex-boyfriend, Joey (Richard Kiley). Joey has told her that it contains stolen business secrets and she believed him, unaware that Joey is actually a communist spy.