 Postal Inspector Dave Webster (Bruce Langley) is riding shotgun guard on a Red River Line stagecoach when it is attacked by two bandits. Sunset Carson (Sunset Carson), Dave s friend and also a postal inspector traveling incognito, is riding inside the stage and picks off the two bandits. Thinking the attack is over, Sunset rides his horse on into town, but the stage is waylaid again by Lon Ballard (LeRoy Mason) and Hackett (Kenne Duncan), and they rob the stage and kill Webster, and push the stage with Webster s body in it, over a cliff into a lake they call the "graveyard." In town, Sunset has an encounter with Julia Bishop (Peggy Stewart)whom he sees later working as a clerk in the Wells Fargo express office. He also connects with  Pop" Underwood (Tom London), saddle maker and veteran postal inspector. That night Sunset finds Julia and Mark Webster (Edmund Cobb), Dave s father, going through his belongings in his hotel room. They escape but Sunset and Underwood also see them the next day near the lake where they have found Dave s hat. She is an Pinkerton operative working undercover with Mr. Webster, a former Pinkerton man. Julia, in her job at the express office, learns that Frank Stevens (Ted Adams), the agent, is working with the Ballard gang. Stevens orders Ballard to kidnap Underwood while he will trap Sunset and Julia, and all three are to be killed and pushed off the cliff into the underwater "graveyard."