The Three Mesquiteers -- Stony Brooke (Robert Livingston), Tucson Smith (Ray Corrigan) and Lullaby Joslin (Max Terhune) -- suspect the unscrupulous Rance McGowan (J.P. McGowan) of supplementing his income by rustling a breed of wild horses protected by the federal government. When Sheriff Miller (Edward Cassidy) gets trampled to death by an unknown horse, the Mesquiteers seek vengeance for his orphaned son. Meanwhile, Brooke angers Smith by courting saloon girl Rita (Rita Cansino).