During the winter season, a family camping in the woods, and a group of camp counselors training in the same forest both find themselves being killed one by one by an unhinged psycho.

On a class excursion to a cave with stone age paintings the clumsy Rex gets lost. A mysterious crystal opens a gateway in time and sets him back to the stone ages, where he meets a group of prehistoric fellows and the gorgeous Eba. While teaching her English and doing some pseudo-research on her fellows, his main goal is to get her sleeping with him. However the curiosity of the clan chief disturbs his attempts.