Hopalong Cassidy, boss of the Bar 20 ranch in Texas, rides down the Camino Real in the New Mexico cattle country near Alamogordo, in response to an urgent message from his lifelong sweetheart, Nora Blake, who is in serious trouble. Before he and his saddlemates, "Lucky" Jenkins and "Pappy", can reach her ranch, they are stopped by Clay Allison, a cattle-rustler who is in almost complete control of the district, and wants to extend his holdings by seizing Nora's cattle and driving her out. Seeing Cassidy as a menace to his plans, he has him arrested on a trumped-up charge. Cassidy and his pals shoot their way out of the trouble and reach Nora;s ranch where they learn that Allison's henchmen have murdered her foreman, Tom Dillon, and Allison has sent for a crew of outlaws on the Texas border.

Hoppy goes undercover as a gambler from the East when Bar 20 cattle are stolen by unknown rustlers. Brennan/Talbot are twin brothers (one a casino owner, the other a rancher) and Hoppy believes they provide alibis for each other while one is out committing crimes. Hoppy gets a job in the casino to learn more but is exposed when a gambling gunslinger notices him.

U. S. Marshals Nevada Jack McKenzie and Sandy Hopkins come upon an overturned stagecoach with the driver and the passenger dead. They learn that the passenger, Hinkley, an archaeologist, has discovered an old Indian site that contains gold relics, and a gang has robbed him of the relics he was carrying. Jane Condon, daughter of Hinkley's partner who was also murdered, tells Nevada that an old Indian guide, Shag, is the only one who knows where the site is. The outlaws find Shag first, and kill him after forcing the information from him. Hinkley's son, Joel, arrives and knows where the site is and leads Nevada and Sandy there ahead of the outlaws.

Belle Starr has returned from time in prison only to face a hail of bullets, along with rescue by Hoppy and the Bar 20 gang.

Hoppy's friend Dennis owns a rich gold mine. Frazier who owns the adjoining mine and wants the Dennis mine, has Dennis killed. Hoppy steps in to take over running the Dennis mine and learns Frazier's men sneak into and work the Dennis mine at night. Hoppy captures one of Frazier's men only to be captured in return by Frazier and left to die in a burning building.

Caldwell and Nixon have their men rob the stage and then critcize the Sheriff for not catching the robbers. With her father the Sheriff under pressure, Mary sends for Hoppy who finds the stolen money and sets a trap to bring in the entire gang.

The local school is causing Hoppy problems. First Bar 20 cattle are stolen when Hoppy investigates a problem there. Then the new teacher arrives and disrupts the routine of the Bar 20 hands. Later with the Bar 20 hands at graduation, the rustlers are poised to strike again. But there is dissension among them and this will lead to the break that Hoppy needs.

Disguising himself as a milquetoast Easterner who writes Western novels, Hoppy enrolls in a dude ranch in order to unmask the murderer of the owner's husband.

Buck Colins heads a group of local ranchers who are trying to prevent the railroad from completing its line through their property. Till now they have been able to charge tolls on herds passing through. Hoppy goes undercover to expose them.

European bad guy Baron Bendor leads some local townsmen in a plot to obtain horses through theft. Hoppy and his sidekicks Lucky and Speedy must find and expose the horse thieves.