West of the Rio Grande plot
"HERE COMES TRIGGER TROUBLE FOR KILLERS OF THE RIO"
City boss Martin Keene is demanding heavy taxes from the residents of Keenesburgh for taking the land he originally sold to them. With an election approaching to determine the county seat, Keene doesn't risk the possibility of Centerville winning, and sends gunman Wade Gunnerson to replace Sheriff Tom Boyd, whom he killed. Once en route, Gunnerson is defeated in a shootout with undercover US Marshal Nevada Jack McKenzie, who then impersonates Gunnerson and joins forces with his colleague Sandy Hopkins to make plans to defeat Keene's gang and ensure fair elections to all townspeople.