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.