Atouk (Ringo Starr) is a bullied and scrawny caveman living in "One Zillion BC – October 9th". He lusts after the beautiful but shallow Lana (Barbara Bach), who is the mate of Tonda (John Matuszak), their tribe's physically imposing bullying leader and brutish instigator. After being banished along with his friend Lar (Dennis Quaid), Atouk falls in with a band of assorted misfits, among them the comely Tala (Long) and the elderly blind man Gog (Jack Gilford). The group has ongoing encounters with hungry dinosaurs, and rescues Lar from a "nearby ice age", where they encounter an Yeti. In the course of these adventures they discover sedative drugs, fire, invent cooking, music, weapons, and learn how to walk fully upright. Atouk uses these advancements to lead an attack on Tonda, overthrowing him and becoming the tribe's new leader. He rejects Lana and takes Tala as his mate, and they live happily ever after.