Undercover Man was the first of the "Hopalong Cassidy" series to be released by United Artists rather than Paramount. William Boyd and Andy Clyde return as saddle pals Hoppy and California, while Jay Kirby is cast as their partner-in-adventure Breezy. This time, Hoppy and company take on a gang of outlaws who've been plying their trade on both sides of the US-Mexican border. The plot is thickened by the presence of a mysterious masked rider who's been impersonating both Cassidy and Mexican police official Gonzalez (Antonio Moreno). Most of Undercover Man is an advertisement on behalf of the "good neighbor" policy promoted between North and South America during the War years.