Cowboy pals Stony Brooke (John Wayne), Tucson Smith (Ray Corrigan) and Lullaby Joslin (Max Terhune) -- collectively known as the Three Mesquiteers -- befriend Ann (Doreen McKay), a pretty, seemingly normal young woman who turns out to be a government agent. Before long, the boys inadvertently get mixed up in all sorts of espionage, including an international smuggling scheme. Things get even worse when Stony is wrongfully accused of murder, and the Mesquiteers must clear his name.