Somewhere south of the Rio Grande at the beginning of the century, Champ Connors is the owner of a huge open air circus that presents remarkable shows as well as historical battle reconstructions between cowboys and Indians. Among the artists, Diana, performs in a particularly difficult show. Tuck Kirby, has left the enterprise to work as a free-lance agent and sells shows to famous characters like "Buffalo Bill".
Diane shows to Kirby her new attraction
When he returns to Connors's circus, it is to propose that Diana work with him. She refuses because she has found a new attraction that will make her a celebrity. Unable to hide her secret any longer, she shows "El Diablo" to her past fiance. It concerns a Eohippus, a kind of tiny horse that existed about fifty millions years ago. The thing is inconceivable, but Professor Horace Bromley, a paleontologist Kirby recently met, confirms it. Wanting to know where the beast was found, Bromley asks Carlos, an important member of the circus who found the horse, but he refuses to deliver this information. Nevertheless, by questioning a group of gypsies, they discover that the Eohippus comes from the forbidden valley.
Prof. Bromley, Lope and Diane
Gypsies feel particularly threatened by the arrival of the prehistoric beast. It represents for them a curse that has to be lifted. Profiting from their beliefs, the Professor invites them to kidnap "El Diablo" and take it back to its initial environment. By secretly following the group, he'll discover the location of the famous forbidden valley that seems to contain so many treasures from the past.
How to take over a pterodactyl...
When the tiny horse is removed, everyone joins in the pursuit. Nevertheless neither Kirby, nor Diana accompanied by Carlos and Champ will succeed in recovering the animal from another era. On the other hand this allows them to discover a fissure that leads to an unexplored valley; the forbidden valley. What they are going to discover there exceeds all understanding. A giant pterodactyl removes Lope, the little boy belonging to the expedition, from the back of his mule. Carlos comes to his help and overcomes the beast, as he is used to doing with his bulls. The Professor believes that seeing this flying reptile is the most extraordinary thing that he has ever seen, then an allosaurus appears!
A strange rodeo
After many attempts and remarkable efforts, and after having been witnesses of a terrible struggle between the allosaurus and a styrathosaur, they finallly capture the beast. The team, minus Carlos who has been killed, returns Gwangi the allosaurus back to town, imprisoned in a cage.
Spoiler ! the end of the story is revealed below…
The first appearance of Gwangi in town rapidly turns into a real slaughter. Helped by gypsies, the beast escapes its huge cage of steel. After having confronted an elephant that belonged to the show, Gwangi leaves the arena of the circus wreaking havoc in the city. The monster follows the residents that flee to cathedral. Its doors are not hard enough to keep the beast out. Citizens flee in terror from the religious monument. After a prolonged struggle, Kirby puts an end to the life of the prehistoric monster when the cathedral erupts into a roaring inferno. With the structure in flames, the prehistoric beast dies as the cathedral falls around him.
Gwangi, prisoner of the flames
(Correction by Dave)