Nugget Clark has been having his stagecoaches wrecked and Federal Investigator Rocky Lane arrives to investigate. The foreman of a nearby mine is stealing part of the mercury output and selling it in Mexico. Nugget's house has a direct pipeline from the mine and they are trying to drive him into bankruptcy to obtain his ranch. Rocky is quickly aware that the Foremen is behind Nugget's holdups but they are also onto Rocky when he accidentally drops his badge during a fight.