A lawyer, running away from his past, becomes a recluse in the Alabama woods and becomes the primary suspect in the abduction of a local boy.

Dr. Clayton Forrester figures he can rule the world if he deadens his subjects' brains by making them endure terrible movies. Exploiting his access to nearby satellite-dwellers Mike Nelson and his robot pals, Crow T. Robot and Tom Servo, Forrester makes them watch "This Island Earth", a cheesy 1950s spaceship film. But when Mike and friends make funny comments throughout the movie and others that follow, Forrester's plan looks increasingly flimsy.

Inventor Goro Ibuki creates a humanoid robot named Jet Jaguar. It is soon seized by an undersea race of people called the Seatopians. Using Jet Jaguar as a guide, the Seatopians send Megalon as vengeance for the nuclear tests that have devastated their society.