I've watched a lot of movies lately that were made during WWII and deal with Nazis and spies. Some are clever and engaging; this one is a by-the-numbers plot with the cheap production values you've come to expect from Monogram.
The "McGuffin" of the plot is a bomb in a suitcase, which has been mistakenly switched with a suitcase full of Nazi spy information. Of course, the bomb ends up on a moving train, which the director reminds us of incessantly with shots of the bomb-laden suitcase superimposed over a moving train. There is little actual tension on board; it's more like a commedia dell'arte farce with people moving in and out of various rooms, carrying suitcases, tying people up, etc.
The Nazi spy ring is full of dopey-looking American actors. How can we tell that they are Nazis? Why, they use the required words "dummkopf" and "schweinhund," and do a lot of bossing other people around.
The B-grade cast has virtually no chemistry. The "romances" and "buddy plot" never really click. There are so many GOOD WWII spy films; don't waste your time on this predictable potboiler.