Terror on a Train, a.k.a. Time Bomb with Glenn Ford from '53.
A mediocre drama about a terrorist who plants a bomb on a train full of sea mines. Glenn Ford is brought in to locate and defuse the bomb before it destroys a town. Apparenly in wartime England there were no local sappers to do the job.. Ford was his usual cool/wooden self, the supporting English casting was good.
We never found out the who exactly planted the bomb or why. The trite ending with Ford walking off with his wife is glaringly undermined by the fact that these two couldn't stand each other and his wife leaves him at the beginning of the film for fun and frolicking in France! The bomb scare prevented her from catching a train or cab to the nearest airport.