Slim Evans and His Horse Lightning

Slim Evans receives a secret letter imploring him to help out as a cattle detective. On his way to the town that is having trouble he hears gunshots and sees two men shooting at someone among the rocks. Slim scares them off by shooting one in the elbow. However as the duo runs away they steal his wonderful horse Lightning while he is meeting the man they were shooting trying to shoot. This man has also received a secret letter so they team up to stop the cattle rustlers - and to get his horse back.