The Narrow Margin

The Narrow Margin is a 1952 American film noir directed by Richard Fleischer and written by Earl Felton, based on an unpublished story written by Martin Goldsmith and Jack Leonard. The screenplay by Earl Felton was nominated for an Academy Award.

Detective Sergeant Walter Brown Charles McGraw of the Los Angeles Police Department and his partner are assigned to protect a mob bosss widow, Mrs. Frankie Neall Marie Windsor, as she rides a train from Chicago to Los Angeles to testify before a grand jury. She is also carrying a payoff list that belonged to her murdered husband. On the way to pick her up, Brown bets his partner and friend, Sergeant Gus Forbes Don Beddoe, what she will be like Shes the sixty cent special. Cheap. Flashy. Strictly poison under the gravy.As the detectives and Mrs. Neall leave her apartment, they are waylaid by a mob assassin named Densel Peter Virgo. Forbes is shot to death, but Densel, although wounded by Brown, escapes. At the train station, Brown discovers that he has been followed by gangsters Joseph Kemp David Clarke and Vincent Yost Peter Brocco. The latter meets him on the train and unsuccessfully tries to bribe him. ........

Source: Wikipedia