When John Robinson loses control of his spacewalk and falls onto a nearby planet, Dr. Smith, in command of the Robot,
immediately tries to force Don and Maureen into returning to Earth rather than going after John. Thanks to some quick
thinking, Smith's takeover is thwarted and the Jupiter-2 braces for a crash landing. Finding the planet cold but
habitable, Don and the Robinsons venture out in their chariot to find John, believing they've left Dr. Smith under
control. They haven't, and the scheming Doctor continues to lay plans with the Robot against the Robinsons.