The Badge of Marshal Brennan

When a gunman, on the run from the law, comes upon a dying U.S. marshal, Matt Brennan, he takes his badge and adopts his identity. In the nearby town of Banock, Dr. Steve Hale fears that he is facing an outbreak of an epidemic when an Indian's son dies under mysterious circumstances. The town derives most of its meat and dairy products from the herds owned by cattle baron Col. Doniphan and his son Shad, and Steve suspects that their cattle are possible carriers of a disease... (official distributor synopsis)