Before landing on the planet, John wants to send the Robot down to check out the conditions. Doctor Smith reminds the Robot to accept only his voice commands. John asks Smith if the Robot is ready to go, Smith tells John he is still malfunctioning. John insists that someone has to go down and scout around. Don volunteers but Maureen reminds everyone that they have an environmental control expert (Smith) onboard. Smith agrees with Maureen but says he can't go because of his acute batophobia.
John decides to go himself using the Para Jet. Will joins the Robot and Smith as they play a game of chess. Don monitors John's decent. He tells John to fire his Para Jets to slow the acceleration. The Para Jets are malfunctioning and do not fire. The Doctor tells the Robot to check on his safety every hour on the hour. Don tells John to use his auxiliary power tanks. John keeps repeating "I can't" until they lose communications. Smith tells the Robot that he will offer the widow his condolences.
Smith suggests to Don that the Para Jets must have been damaged in the meteorite storm. Don says he checked the Para Jets and they were working fine. Penny says she seen Smith checking them too. Don asks Smith if he tampered with them, Smith suggests that Don should concentrate on John. Don tells everyone to prepare for a landing. Smith thinks now that the ship is 200 pounds lighter, they should try to make it back to Earth. Smith threatens to have the Robot crush Don's head if they don't leave for Earth now. Don gets Smith in a headlock and has him order the Robot back to his compartment. Don puts Smith into a freezing tube, Smith says something about the rockets before being frozen. Don and Maureen try to fire the braking rockets but find they are malfunctioning, Don thinks Smith has sabotaged the rockets. Maureen goes to the lower level and straps in. Don gets into a freezing tube just before the ship crash lands.
Everyone in the lower level is okay. Judy rushes to the upper level and gets Don from the freezing tube. Don tries to decide what the next step should be. Will suggests that he may be able to get the Robot to listen to him. In a voice similar to Smith's, Will commands the Robot to go outside the ship to check the conditions. The Robot obeys. The Robot reports that the environment can support human life. They decide to assemble the chariot to move over the rough terrain. They leave Smith in the freezing tube as the head out in effort to find and rescue John.
They pick up a signal on the scanner coming from straight ahead. They come to a wooded area, and Don gets out to search for John. He sees some bushes moving up ahead, he rushes over to find a chimpanzee-like creature that makes "bloop-bloop" sounds. He brings it back to the chariot while not too far away John lays dangling in a chasm. Penny immediately adopts the creature and calls it Debbie.
Maureen calls John on the radio, as John reaches for his walkie-talkie it gets fried by an electric field. As they get ready to leave, Judy points out that the signal is still on the scanner. Don goes looking again. He finds John, calls for the Robot to come with rope. Will instructs the Robot to help Don rescue John. The Robot heads back towards the ship stating he must check on Smiths safety every hour on the hour. Judy takes the rope to Don. Don lowers the rope to John and pulls him up to safety. After talking with each other, both John and Don conclude that Smith tampered with the ship's rockets as well as the para jet's rockets.
The Robot returns to the ship where he releases Smith from the freezing tube. With Don and the Robinsons off the ship Smith decides it is time to take the ship back to earth. Back in the chariot, Don and the Robinsons head back towards the Jupiter 2. The chariot almost runs into a giant electrified tumble weed which drains all the power. John decides they should all walk back to the ship. Smith is angry that the Robot can't pilot the ship. Smith tell the Robot that he needs Major West to pilot the ship, that the Robinsons serve no purpose and should be liquidated. He tells the Robot to pick them off one by one.
The Robinsons return to the ship, the girls go to the lower level to cook dinner, Don and John work in the upper level. Smith tells John and Don that he has had a change of heart and wants to help. Don doesn't believe it. John fill out his daily log. Later everyone gathers for dinner, all but Will. Penny tells them Will went back to fix the chariot. While at the chariot, Will hears the Robot approaching. The Robot goes through its programming, Eliminate all non-essential personnel.