When the story begins, a Constable finds a man up to no good a the rail yard. At first, he just assumes it's some hobo riding the rails, but after a scuffle they find detorators where he guy dropped them. Obviously, he was saboaging the munitions train. The problem is that it's a big train and there just isn't a lot of time to find the bomb before it explodes....if there is a bomb.

If happens that Peter (Glenn Ford) is a bomb disposal expert and he's nearby. So the police rush to get him to the train and evacuate the area why he does his work. What's next? See the film.

If you want a film with a lot of tension, this movie is a very good choice. While the plot is pretty simple and you have no idea why the bomber did what he did, the payoff at the end is there...and the film very well made.