Atouk (Ringo Starr) is the leader of a small band of misfit cavemen who are part of a larger community headed by strongman Tonda (John Matuszak). Atouk is madly in love with Tonda’s woman, Lana (Barbara Bach). He even ignores the advances of the lovely Tala (Shelley Long) and sets his mind to finding some way of wooing Lana. During Atouk’s quest for romance, he and his cohorts fend off dinosaurs, indulge in hallucinogens and invent cooking, music and medicine.
Buckaroo Banzai is caught with his trusted allies, the Hong Kong Cavaliers, in a battle to the death between evil red aliens and good black aliens from Planet 10. Led by demonic dictator John Whorfin, who has taken over the body of Italian scientist Dr. Emilio Lizardo, the aliens try to get the Overthruster back from Buckaroo Banzai. But the good black aliens are willing to destroy Earth rather than let these renegades return to their planet.