The Bar 20 boys are after Nevada and his gang of cattle rustlers. Hoppy and California join Nevada's gang under assumed names. Johnny and the rest of Bar 20 get directions from Winters and head out looking for Hoppy's signal. But Winters wanders on ahead and gets spotted. This lets Nevada trap them in a canyon and to make matters worse, Hoppy's masquerade has been exposed.

While searching for an outlaw named Nevada, rancher Hopalong Cassidy and his friend, California Carlson, meet with Verde saloon owner Long Ben, a former outlaw whom Hoppy once ran out of Santa Fe. Although Ben resents Hoppy, he betrays the location of Nevada's hideout in Snake Buttes because Nevada's gang robbed him after he beat them at cards. California and Hoppy, posing as notorious outlaw Tex Riley, ride to Nevada's hideout and join the rustlers. Their pal, Johnny Nelson, meanwhile, meets with the local ranchers, who form a posse to go after Nevada and his gang. Elderly prospector Jud Winters joins them, as does his granddaughter June, who worries about her grandfather's health. At the hideout, petty rivalry in Nevada's gang results in several shootouts among the men, and Hoppy uses the diversion to set a slow-smoldering signal fire for the ranchers. Hoppy also becomes embroiled in the rivalry and kills a rustler in self-defense. When the fire erupts full force, the Chinese cook is blamed, but the ranchers see the signal and ride toward the hideout. Nevada becomes suspicious of Hoppy because his recent problems seem to point to him. Just then, two rustlers sight Jud, but after they find the ranchers, they are both killed in a shootout. Nevada sends one of his men to see Ben, who is murdered after telling the rustler that Hoppy is an impostor. The outlaws hunt down the ranchers and engage them in a gunfight, first at the ranchers' campsite, then at a box canyon where they entrap the ranchers. However, Hoppy and California capture the men guarding the trapped ranchers and rejoin their friends. When the rustlers return, the ranchers are fortified, and during the ensuing gunfight, the rustlers are killed one by one. Hoppy and Nevada then face off, but when Nevada draws his weapon, Hoppy shoots him. All the cattle are returned to the ranchers, and Hoppy, Johnny and California return home to their own ranch.