Pony Express rider Sunset Carson, making his last trip, reaches his final station and finds the attendant has been murdered. Sunset is ambushed by three masked men, who take one letter from his pouch and leave him for dead. When he arrives in Big Rock Springs, he apologizes to Martha Taylor for not having her stolen letter, and when she and her brother Tom, offer him a job at their ranch, he accepts. Sunset suspects that the mysterious doings at the ranch has something to do with Western Union stringing its wires across the Taylor ranch. He eventually proves that neighboring rancher Spade Gilbert and Grand Dawson are behind the scheme to keep the Taylor's from landing the Western Union project.