After Roxy Miller encounters the enormous caveman Eegah while driving down a remote California road, her father, Robert, sets out to the desert to prove his daughter's claims are true. Once there, Robert is knocked unconscious and trapped in Eegah's cave, where he gains insight into prehistoric life. However, when Roxy and her boyfriend, Tom, come to rescue Robert, Eegah grows fond of the girl and refuses to let her leave.