Under the leadership of a cutthroat named Grif (Dick Curtis), a band of outlaws has systematically been robbing and murdering settlers bound for the large Chandler ranch which has been cut up into small parcels of land for purchase. The postmaster, and operator of the Three Monkeys Saloon, Harvey Grimes (Alex Gerry) opens all mail addressed to Nugget Clark (Eddy Waller), foreman of the Chandler ranch, and is able to tell who is coming to buy land. He passes the information along to the outlaws and they bring their hauls back to him. Some of the settlers are clients of the Mohican Insurance Company, which sends their ace agent, Rocky Lane (Allan Lane) to investigate. Rocky finds a piece of a watch fob that links Brag (Pierce Lyden), one of Grif's men, to the recent killing of a settler. When Brag becomes unduly nervous, Grif shoots him and lays the blame on Rocky, posing as an itinerant cowhand. Roy Chandler (Byron Barr), heir to the Chandler ranch, is a witness and is kidnapped and held captive in a hideout. Rocky reveals his true identity to Nugget and Gail Warren (Lyn Thomas), who innocently puts his life in danger just as he is about to unravel the mail-tampering scheme.