Because the Panhandle Cattle Association refuses to send out cattle until they are bid a higher price, Hopalong Cassidy and his neighbors start a trail drive to bring cattle north, but unknown to Hoppy, two rivals sign up with them, Tex Anderson and Joe Wilson, who intend to delay Hoppy's herd so that their own cattle, headed by their boss Lewis, will arrive first. One day, after Hoppy and his ranchhand Johnny Nelson rescue Beth Clark, who was thrown by her own horse, she reveals that her father, John Clark, whose job is clearing trails for cattle drives, has been missing. Hoppy has been dealing with a trail cutter who is actually an accomplice of Tex, but Hoppy refuses to allow him to delay his drive. One night, when rustlers attack the herd, the chuck wagon is set on fire and all their provisions are ruined, and Hoppy realizes that one of his men is working with the rustlers. Hoppy and his sidekick Windy are forced to get provisions from Waggoner, a longtime rival of theirs. While they are busy getting provisions, Johnny conducts an investigation of his own and captures one of the rustlers, who reveals that John Clark was captured by Lewis, head of the rival cattle drive. That night, two of Hoppy's men are mysteriously killed, and although he suspects Tex, Hoppy releases him due to lack of evidence. Beth rides ahead to Plainsville to get help, while Hoppy starts a brush fire, hoping to prevent Lewis from sending his herd ahead, which is against trail regulations. Meanwhile, Wilson steals dynamite from Hoppy intending to explode it at the mouth of a canyon just before Plainsville. Hoppy intercepts the dynamite, however, shooting both Wilson and Tex in self-defense, and then rescues Windy, who has suffered a gunshot wound during a shoot-out. The herd reaches Plainville, and Hoppy heads south to Mexico, his friends joining him along the way.