The government assigns cavalry captain Bob Bradley (Bob Baker) to an area where pony express riders are being killed by arrows and their mail is being rifled. Posing as horse buyers, Bob and his pal, Andy Sharpe (Don Barclay), center their investigation around the ranch owned by Don Ricardo Hernandez (Martin Garralaga) where, in addition to learning that the Don has a pretty daughter named Lorita (Cecelia Callejo), he discovers that Jack Sommers (LeRoy Mason) and his lead henchman Phelps (Jack Kirk) are getting possession of the huge ranches, created by Spanish land grants, by having Ramon (Carleton Young), a disloyal Hernandez servant, kill the riders with arrows (hoping the Indians will be blamed) and taking the certificates of registry.