Professor Robinson is caught in a matter transfer emission ray, and subsequently ends up in another dimension where he is confronted by a version of himself and Don. However this realm is the opposite of his own dimension, the anti-matter world, where everything in reality is twisted. The evil John returns to the family and attempts to take over the Robinsons and take over John's life. Will he get away with it, or are Will and the Robot able to defeat him, and restore the world to it's natural order.

Lost in Space's only Christmas program. Will uses an alien transporter to send himself back to earth. However, many people believe the Robinson family to be dead after hearing the ship went off course. Nobody on Earth believes him, and they lock him up with the intention of sending him to a boys' home. Will escapes the family home he's in, and wanders around these clueless bunch of townspeople, but finds carbon tetrachoride — needed for the food processors on the Jupiter. Eventually he convinces another boy, Davey, to let him out, and let him return to the planet he came from. He returns to Priplanus with this bottle. Of course no one believes his adventures until he produces the bottle, plainly labeled as coming from Earth.

The Keeper, played by Michael Rennie, is a zoo keeper. He wants to take the children and add them to his collection. This episode is the only two-parter from the series.

John Robinson is possessed by an alien spirit. The alien forces the family to prepare to return to the spirit's home world, even if it requires he sacrifice Will to keep his secret from the rest of the family.

Professor Robinson discovers that the planets orbit will bring immense heat on the spaceship. With that knowledge the Robinson's take off in the chariot and head south. However back at the Jupiter two, Dr Smith who stayed behind because he believed them to be lying, realises that the orbit is strange, bringing immense cold followed by extreme heat. He sends the Robot to tell them, and they then attempt to travel back to the Jupiter 2. However in their way is a huge in-land sea which previously had been frozen solid. The immense heat and cold make the vegetation charred. They survive the heat and return to the Jupiter Two where they are most safe.

The Robinson family banish Dr. Smith from the Jupiter 2. He takes refuge in an abandoned spaceship where he finds a machine that can materialize anything. In an attempt to get back on the Robinsons good side he gives them the machine which plays on the family's greed.

Will and Dr. Smith stumble upon another robot. More capable than their own robot the alien robot works to gain the confidence of the Robinsons. At a critical point he plans to transport them to his home planet as slaves.

In the year 1997 the Robinson family take off to colonize Alpha Centauri. A spy from a foreign country AKA Dr. Smith becomes trapped aboard trying to sabotage the project. The ship is whisked off course and into a meteor storm due to Dr. Smith's extra weight upsetting the navigational computers. Smith desperately tries to save himself by reviving the crew. The result: the Robinson family becomes lost in space.

Penny "imagines" a new companion, which is a disembodied life force living below the surface. Dr. Smith accidentally injures Penny, leading to the creature taking his anger out on the entire planet.

The second part of the zookeeper played by Michael Rennie. Rennie turns in a memorable performance as The Keeper. His understated performance keeps dramatic tension where none would probably exist with a lessor actor.

Luminous aliens capture Dr. Smith and plan to replace their burnt out computer with his brain. Smith bargains with them and they attempt to use Will's brain instead.

The Jupiter 2 and all aboard are caught in a space 'time-warp'! After everything seems to return to normal, they're shocked to find Earth within their reach and decide to return home. Though they're perplexed that they are unable to contact 'Alpha-Control', they decide to land in the 'good ole USA' ....only to find it's 1947! As usual, Dr. Smith causes issues & even considers staying behind when the Robinsons and West announce plans to leave.

John discovers that the planet they are on will travel further from the sun.In an attempt to survive the Robinsons pack up and head south. Dr Smith stays at the Jupiter 2 site while the Robinson family encounter a terrifying cyclops and an ancient deserted city.

An alien boy is sent to Priplanis to validate his prince status. Will is drawn into a battle to the death unbeknowest to his father. Once his real intentions are known John substitutes himself in the challenge and the Alien Ruler substitutes himself for his son.

Professor Robinson attempts to explore a planet that the Robinson's are planning to land on. His para-jet propulsion system fails due to sabotage by Dr. Smith. Major West "lands" the Jupiter II, in spite of the fact that Dr. Smith has also sabotaged the propulsion system of the Jupiter II, and the family and Major West rescue Professor Robinson.

The Robinsons and Major West are imprisoned in their camp, after being indited to appear before the a trial in court space crimes. As the trial begins, Dr Smith's name begin's to appear and it is not long before it is realised that all of the Robinson's crimes are due to Dr Smith, and he is indited to appear before the court. Will he be found guilty?

With the power source of the Robinson's at a low, they are unable to recharge the Robot. As a result of this the Robot leaves the group, not wanting to be a further burden to them. When they later change thier minds, they cannot find the Robot. Will and Dr Smith discover late one night, but due to the gases in the area he has grown to be bigger than a house. Will decides to only way to reverse the process is for them to go inside him, and work it internally. Will they get out in time?

Dr. Smith, Will, and the Robot are accidentally launched in the Space Pod. They land on a planet that is controlled by an alien machine that creates illusions to confuse visitors and drive them away. The Jupiter II lands and rescues them, and the robot destroys the alien machine.

Penny and Judy stumble upon a mirror. They discover someone is on the otherside. Before they know it they are transported to the mirror universe which is occupied by only one person, a boy who is lonesome for companionship.

In this retelling of "The Midis Touch", Dr. Smith gains the power to turn anything into platinum. Penny is given a gift by a thief on the run, who tells her to protect it for him. She and Dr. Smith discover that it leads them to a ring which, when worn, allows the person to turn anything to platinum, which Dr. Smith does and enjoys. However, when it turns even his food to platinum, he is unable to remove the ring, which is now a solid bar. He leaves the camp as he fears turning everything into platinum, and he will eventually starve to death. A galactic lawman is on the trail, looking for the stolen device to use for his own nefarious purposes.

The beginning of the third season finds the Robinsons having to quickly leave the planet they are on, which is a similar plot to the beginning of the second season. Once in space, the robot is swept overboard and has to be rescued. Then the Robinsons find a prison ship filled with cryogenically preserved prisoners. The prisoners have been interred past their normal sentences due to a malfunctioning timepiece on the prison ship. Professor Robinson repairs the timepiece and frees the prisoners. Robby the Robot makes another appearance, threatening Professor Robinson and Major West.

A strange blue fog seems to be engulfing the Jupiter 2 periodically. Dr Smith and Will commment seperately that they want to be left alone. When the members of the Jupiter 2 begin to randomly disappear as the fog comes, Dr Smith thinks he is to blame. Eventually Will discovers a strange creature which takes over Dr Smith. The creature tells Will that he is his own Id. Will finds out his Id is a creature he created full of Will's own personal demons, thoughts, feelings and insecurities. Will defeats the creature by overcoming his ""fears"" and throws the powerless creature in the power core. The members of his family are returned.

Will is conducting an experiment in a cave and captures a man who claims to be the man who controls time for the entire universe. This ""Time Merchant"" takes Will, Professor Robinson, Smith, and the Robot, to his secret lair. From there, Smith uses the Time Merchant's time machine to return himself to Earth on the day the Robinson's departed, with the objective of NOT sabotaging the Jupiter II mission and letting the Robinsons go on their way to Alpha Centauri. The Time Merchant then announces that if Smith does not get on the Jupiter II, the ship will not fly off course and will therefore be destroyed by a collision with an asteroid several months after liftoff. So Will is sent back to join Smith and try to convince him to get on the Jupiter II as he originally did.

The Robinsons can not understand the language of a visiting family also on the planet. The aliens are called Taurons, and come to use the planet as a new colony. However Dr. Smith causes problems between the two camps when he panics and draws a gun on the new family. The Taurons end up not liking the planet and want to be alone, so they leave.

Dr. Smith is conscripted as the leader of a people from another world. Little does he know that the leaders of these people are routinely sacrificed and replaced with other expendible leaders. Smith is just one of a long line of sacrificed rulers.