Synopsis: Cowboy pals Stony Brooke, Tucson Smith and Lullaby Joslin -- collectively known as the Three Mesquiteers -- befriend Ann, 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.