The film begins with lots of character development and little involves the historic figure of the title. Eventually, it gets around to portraying Mosby's famous raid in which he captures Union General Edwin H. Stoughton and dozens of prisoners.
The raid, conducted well inside Union territory, was spectacularly successful and ended with no shots being fired. Unfortunately, because Mosby is not the focus of the film, the interesting history is largely glossed over. The film concludes with Corporal Jenkins' romance with Willie's sister, Oralee (Lipton) setting the stage for a Union attempt to trap Mosby's men.
The film's treatment of the Confederates is moderately sympathetic. The primary villain is a spiteful Union sergeant (Adams) who can be counted on to make the expedient decision over the honorable one. Most characters on both sides are reasonably human with the expected flaws. Both Willie Prentiss and Henry Jenkins are confronted with having to decide between friendship and duty.
If the viewer is expecting a good or complete portrayal of the exploits of John Singleton Mosby, it won't be found here. As a family oriented Civil War film, "Mosby's Marauders" is passable, but Disney has done far better with other live action films.