 In circa-1900 Mexico, T.J. Breckenridge, a beautiful cowgirl, hosts a wild west show that is struggling. Former boyfriend Tuck Kirby, working for Buffalo Bill s wild west show, wants to buy out T.J., but T.J. has an ace she hopes will boost attendence at her show - a tiny horse. The tiny horse, however, comes from The Forbidden Valley and a convoy of gypsies demands the tiny horse be returned to the valley; the horse s genesis is also known to a British paleontologist, Sir Horace Bromley, working in the nearby desert. T.J., her men, and Tuck eventually find The Forbidden Valley with Bromley, and encounter a litany of living dinosaurs. One, a belligerent Allosaurus, is known as Gwangi by the gypsies, and a running pursuit sidetracks into a bloody battle with a styracosaur and eventually to terror in the outside town.