Forget the remake with Gene Hackman, the original The Narrow Margin (1952) is one of the top ten film noirs ever made, anywhere, anytime. And the greatest part of the film is aboard a train. Even better, for us FRNs. Charles McGraw can play it good or bad and in this film he is a cross between the two (maybe his best placement yet), and a cop. He's tough with everyone until he meets his match — one Marie Windsor.
Back to the train. It's a Richard Fleischer film, without a doubt his best, and there's a slain gangster's widow to protect (enroute to a trial) with 2000 miles inbetween (Chicago~LA). Back when they used to know how to edge a film in black and white, all at a crisp 71 minutes. No fuss, no muss.