With a crew of killers masquerading as ranch hands, Simon Miller runs a large ranch near Mesatown, while his henchmen carry out his plan to steal all of gold-bearing property of his neighboring ranchers. Johnny Mack Brown, Interior Department agent, arrives with the news that the entire territory is to be thrown open for homesteaders, and Miller and his gang resolve to keep them out. Panhandle Jones and his wife Nora, old retainers of the formerly-honest Miller, secretly write to the latter's grandson, Terry Draper, hoping he can bring the old man to his senses. Terry joins the Dalton wagon train to the Mesa Territory after marrying Dalton's daughter Jennifer. Two of the outlaws meet the train, pretending they are guides sent by the government, and they poison the horses and the wagon train faces disaster. Not realizing that Mesatown is just a short distance from them, Terry takes an empty wagon to get supplies and horses, and one of the outlaws goes with him, and kills him on the train. Johnny finds Terry's body and his diary and rides to town, where he and Panhandle kill or capture the entire gang after a gunfight. Miller sees the error of his ways, and throws open his land to the settlers.