In the Southern Mexican jungle, an adventurous archaeologist is accompanied by an equally daring female photographer in a search for a lost Toltec city. They engage a guide to lead them on their expedition, and soon find themselves in the jungle's depths, far from civilization. Soon both the guide and the archaeologist are vying for the affection of the photographer. They must all deal with enormous danger and sacrifice before their quest is complete.

A college paleontology professor acquires a newly discovered specimen of a coelacanth, but while examining it, he is accidentally exposed to its blood, and finds himself periodically turning into a murderous Neanderthal man.