Longley has been made a special marshal to the Texas town of Rio Nada. The area has been plagued by Mexican bandits who have used it to cross the border into the United States and raid the countryside. The gang is led by a mysterious leader known only as "El Sombro". When Longley captures an agent for El Sombro, he hopes to use the threat of hanging for the attempted murder of a deputy sheriff to force him to identify the illusive bandit chief. (Note to viewers: Best to first view "The Terrified Town", then "Sixgun Street", then "The Taming Of Rio Nada", as this is the order in which the events are meant to take place even though the episodes originally aired in the reverse order).

After acting marshal Bill orders no guns to be worn on the streets of Rio Nada, a local casino owner sends for two notorious gunmen to kill him.

Bill finds a town engulfed by a feud between two ranchers. He also learns that his former commanding officer, now a doctor, has turned to drinking, and that a young man blames him for crippling his arm. Bill tries to talk the doctor into staying and not running from the challenges.