When a mobster's widow decides to testify and provide names of others involved in evil deeds, she goes undercover to avoid being killed. Onboard a train going cross-country, she's being escorted in order to testify. Cop Walter Brown and his partner are assigned the task, but the mob are on their trail, attempting to make sure she never reaches her destination.
The Narrow Margin
A woman planning to testify against the mob must be protected against their assassins on the train trip from Chicago to Los Angeles.
