The Robinsons take a boy home to his planet and come across a spaceship that is a space lighthouse. The boy gets angry when they tell him they don't have enough fuel to get him home.
Intergalactic showman Farnum B captures humans to exploit for the amusement of aliens. Among the new exhibits in his star-spanning zoo are Will, Penny, Don, Judy, Dr. Smith, and Robot.
John Robinson and Don West are transported onto a strange new world where their evil opposites exist and plan to change places with them. Will, the Robot and a reluctant Dr. Smith set out to find and help the real Don and John only to be pursued by an evil John Robinson.
Landing on a planet some shapeless beings duplicate the Robinsons and take the Jupiter 2 with the intent of conquering Earth. Will gets aboard to stop them.
After making a deal with the Time Merchant, Dr. Smith returns to Earth just before the launch of the Jupiter II. If he doesn't get on it, the Jupiter II will crash into an asteroid.
When the Robinsons nearly reach Alpha Centauri, they find a human base run by young people. They convince the adults that Penny and Will aren't their children and they leave in the Jupiter 2.
Farnum B, the intergalactic showman, again encounters the Robinsons as he presents the Galaxy Beauty Pageant, and its sponsor wants Judy to enter - and win.
Smith lands the pod on a planet where plants are the highest form of intelligence. The Robinsons land only to be captured by Tybo, a giant carrot. He plans to turn them into trees while Dr. Smith becomes a stalk of celery.
