In this 1940s serial, someone is attacking Pony Express riders on the Overland Mail route, and it's up to Frontier Marshals Jim Lane and Sierra Pete to find the culprit. They know a local Indian tribe is carrying out the attacks, but they suspect someone else is driving their actions. As the attacks become more frequent, it's a race against time to nab the perpetrator before anyone else loses their life. Lon Chaney Jr. and Noah Beery Jr. star.