 In this 14th film of the 66-film series that is credited on the film as being based on Clarence E. Mulford s novel "Tex"... but isn t, other than some character names...the United States Army needs horses for the Spanish-American war but all attempts to get wild horses from the Western plains has failed as the gathered herds have been taken by rustlers. Colonel Whitely (Earle Hodgins) instructs Major McCready (Karl Hackett) to secure the services of Hopalong Cassidy (William Boyd) who, meanwhile, has been training his men as a volunteer force. While disappointed at having to work as a civilian, Cassidy answers the call to the flag and with the help of Lucky Jenkins (Russell Hayden), Windy Halliday (George Hayes), Smokey (John Beach) and the other cowhands, rounds up a herd of 500 wild horses. Black Jack Carson (Alexander Cross) and his henchmen Hawks (Bob Kortman), Shorty (Jack Rockwell) and Brad (Ray Bennett) steal the horses and capture Cassidy and his men. With the help of Boots (Billy King), the Colonel s son, and Barbara Allen (Judith Allen), Lucky s sweetheart, Cassidy manages to escape, regain the horses and capture Carson and his men.