 Poor old Granny Phelps inherits the Circle H Ranch where the Three Mesquiteers work. The boys are rounding up horses to bid on the upcoming Army contract. Martin, trying to assure himself of the contract, has two of his men working on the Circle H. When they kill a man the boys find themselves in jail. The race for the contract is about to start and Stony is needed. So old Granny heads to the jail to break them out.