During an expedition into Central Africa, paleontologist Dr. Susan Matthews-Loomis (Sean Young) and her husband George Loomis (William Katt) attempt to track down evidence of a local monster legend. The monster, which the local natives refer to as Mokele-mbembe, shares many characteristics with the Sauropod order of dinosaurs. During the expedition, they discover Brontosaurs in the deep jungle and are further amazed when the animals show very little fear of them. The couple begins observing the creatures and become especially enamored with the curious young offspring of the pair, whom they nickname "Baby". Unfortunately, the discovery soon places the dinosaurs in jeopardy from both the local military as well as fellow scientist Dr. Eric Kiviat (Patrick McGoohan).