Based on the novel by Zane Grey, Western Union tells the story of Vance Shaw, an outlaw on the run who is anxious to shed his criminal past. He gets his chance when Edward Creighton, the Chief Engineer in charge of constructing telegraph poles from Omaha to Salt Lake City, offers him a job protecting the workers against attacks from gangs of bandits. However, Vance's dark past comes back to haunt him when his rebellious brother, Jack Slade, leads an attack on the construction line, pitting brother against brother in the Wild West of America.