Professor Robinson discovers that the planet's orbit will bring immense heat on the spaceship. With that knowledge, the Robinsons take off in the Chariot and head south. Dr. Smith stays behind because he believes them to be lying, but soon realizes the orbit is odd. There are periods of extreme cold followed by equally extreme heat. The Robot is sent to tell the Robinsons and they try to return to the Jupiter 2. They must brave various geographical areas and the strange weather before returning to the Jupiter 2 where they are most safe.