 The Cloverdale stage, its driver and a large payroll has disappeared, with no trace being found by a posse. Pop Warner the driver, known to be in financial difficulties, is suspected, but his daughter Mary (Victoria Vinton), knows he is innocent. Insurance investigator Ted Sanders (Bob Custer) finds Warners s body in a revine, with Rannah (Rin-Tin-Tin, Jr.) watching over the body of his dead master. Ted finds the buried remains of the auto-stage, but no trace of the missing money. While Ted is conferring with Frank Norcross (Roger Williams), the banker who sent out the payroll, an attempt to shoot Rannah is made from outside the window.Ted thinks that Rannah can lead him to the killer. That night, Ted captures a mysterious stranger (Ed Cassidy) outside his cabin, who says he is Deputy Sheriff Barlow from the county seat and they agree to work together.Mary phones there are prowlers around her ranch, the deputy hears the call and slips away. Ted rides to Mary. The deputy arrives first and he and the men ambush and tie up Ted and enter the house to kill Rannah. The dog escapes and finds and frees Ted. Ted and Rannah find a wounded man (Wally West) and Rannah tries to attack him.Ted takes him to Doctor Adams (John Elliott) and the man tells Ted he is the real Deputy Barlow, shot by the outlaws and his identification and clothes taken and others substituted. He believes Rannah attacked him because he was wearing the real assassin s clothes. Ted asks the Doctor to hold an inquest, where he proves that the fake deputy is an henchmen named Sam, working for Norcross who was the brains behind the robbery.