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.

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.

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 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.

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.

Dr. Smith holds a seance to contact his Uncle Thaddeus. Instead a spirit creature is contacted and creates havoc for the Robinsons. It is later discovered that the ""spirit creature"" is a physical creature, rendered invisible by the properties of the ""ionized gas"" in the bog from which it came.

While playing a outdoor match, Will and Smith's ball explodes, and as the smoke clears there ball has turns into gold. the ball rolls into the cave which has 3 aliens inside, the alien wants the robot , which is later stolen when Will refuses to let them have it and Smith does. Can the crew get there robot back.

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.

The women of Lost in Space are featured in their very own episode while the boys are out installing communications equipment. Smith is left in charge (boy is that a mistake) and he "cleans" their weapons, but cannot remember how to rebuild the weapons. This leaves the J2 crew defenseless. A creepy creature stalks the Robinson women however they think a small dog is to blame for raids on food and other mischief.

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.

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 Jupiter 2 is pulled into a giant alien spaceship where there are advanced bubble-like creatures. While John and Don look for maps and equipment Dr Smith and Will look for trouble.

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.

Will and Dr Smith discover an old, abandoned Android Machine. When Dr Smith plays with the buttons on the machine, he accidently orders an Android. He thinks he has it for free, and uses her as his personal slave, assuming she has no human emotions. What will he do when the owner, Zumdish, and his guard turn up...demanding payment?

When Dr Smith's cousin Jeremiah Smith arrives on the planet, everyone welcomes him, except Dr Smith. Dr Smith alienates himself from the family, and refuses to return until his cousin leaves. It is later discovered that Jeremiah's reaosns for being on the planet are far deadlier than anyone imagined.

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.

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.

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.

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.

The Robot suddenly announces that the Jupiter II is approaching Alpha Centauri. Everyone is suprised, and the ship lands on a planet, where they are greeted by a group of people who appear to be teenagers from Earth. It turns out that they are aliens who live like Earth-style hippies, and they are incapable of growing old. They want to age normally, and to do this they want to get the older members of the Robinson party to leave in the Jupiter II while the younger members can stay behind and be used in an experiment that will make it possible for them to do so. The aliens trick the older members of the Robinson party into leaving, but Will pulls a fast one on the aliens and the Jupiter II eventually returns to the planet, and Penny, Will, and Dr. Smith, who somehow passed himself off as a young person, are rescued.

When a troope of Galactic Gladiators arrive on the planet, they challenge Professor Robinson to a duel, which will be aired all of the galaxy. John declines saying he isn't interested in physical combat. Dr Smith takes up the offer when he makes a deal that if he wins, he will be returned to Earth. Unbeknownst to him, if he loses, which is a near-certanty, Earth will be destroyed.

The Space Pod lands on a planet that is inhabited by creatures who all look alike, and aspire to be different. They capture the Robinsons and make duplicates of them with the objective of using the duplicates to fly the Jupiter II back to Earth. Will is not duplicated, and he thwarts their plan.

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.

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.

Dr. Smith eats some alien fruit which transforms him into a giant. Convinced it was the Robinsons trying to kill him, he plots to take them out.

Dr. Smith's finds an alien ship and wants to use it to get back to earth, but he doesn't count for the owner of the ship admiral zahik to turn up and wreck his plans.

A storm looms up and the two gloves of Thor appear from space and straight into the waiting hands of Dr. Smith. Then are then taken away to see the real Thor who will decide there fate.

Will and Dr Smith are confronted by a knight, who says he is on a quest to seek out and destroy the beast Gundemar. Penny, meanwhile, meets Gundemar and befriends her. Will becomes the pageboy of the knight. When it is discovered that the beast is woman, the knight is unsure whether he can still kill it, leading him to question his life's future.

The Robinson's communications system is knowcked out, and they discover that the culprit is a female warrior, who is planing on making this planet a colony for her people. She encaptures the members of the Robinson camp, and puts the men to work clearing a landing platform and erecting an arc. Meanwhile she keeps the females seperate and teaches them of the virtues of females, and the vices of males. Dr Smith becomes her escort to get out of work. Just before her colonists arrive, John, Will, Don and Dr Smith destroy the arc, and the colonists leave. It ends with Noble Neolani questioningthe value of men, and perhaps they weren't as bad or stupid as she thought.

The crew are outside playing ball when a magician called Zalto. Dr. Smith uses Zalto to conjure up a space ship so he can use it to get back to earth.

A caveboy appears and attempts to lure Penny away, but she refuses, and is instead caught in a net. She is transported to an intergalactic zoo, were she will be puton show, meanwhile Dr. Smith tries to take over the zoo.

Dr Smith discovers another Android Machine, in the middle of a dangerous fisher. When he tries to order something, he is trapped inside the machine. Later when Will tries to get him out, he too is sucked in. Zumdish arrives on the planet in order to destroy the faulty, forgotten machine. Meanwhile Will and Dr Smith discover the magical Toymaker's world, as they are mistekn for toys. They later discover they are close to earth. Will they return to Earth, be blown up, or Will Professor Robinson and the Robot be able to save them.

The Robinsons take in a Princess who is fleeing from a bounty hunter. Will is captured by the bounty hunter, who wants to trade the boy for the princess. the robot then comes up with a idea to save the day.

Dr Smith is confronted by an identical look-alike called Zeno, who is on the run from the law. Zeno makes him trade places and Dr Smith, out of fear confesses to Zeno's crimes. He is arrested and he and Will taken away to appear in court. Will the real Zeno be caught before Dr Smith is boiled in oil?

Athena the girl from the green dimension who hypnotised Dr Smith during thier space flight arrives on the planet. She still is in love with Dr Smith, which he uses to bribe her to help him see the future. However, he promises to go back to the green dimension with him, and when Athena's previous suitor arrives and turns Will green, Dr Smith must find a way to save himself and Will. Urso, Athena's suitor challenges Dr Smith for the lady, customary in the Green Dimension, and after seeing the future, Dr Smith fears the worst. Athena realises he cannot be with her, and leaves with Urso, but not before Urso restores Will's colour.

Two aliens, who are actually intergalactic bank robbers, transform themselves into Earthlings. They revive a man named Zumdish who operates a tour agency and they pretend to be his clients. The Robinson's head off and Dr. Smith is left alone, Smith's decides to turn the ship into a hotel and doesn't realize how dangerous his guests are.

Dr. Smith answers a distress call from an alien space ship. He arrives there using the Space Pod, and discovers that the aliens want him to operate on (actually, repair), their leader. It turns out that the aliens are a race of some sort of robot that survive as long as their leader, who functions as their central control timepiece, is in working order. The Robinsons come to Smith's rescue in the Jupiter II. The leader is repaired by the robot, and the extended space family Robinson leave the alien space ship safely.

A crew led by Captain Kraspo is searching for the missing Princess Alpha. They bring Will aboard their ship who makes them think the Penny might be there princess, because of this the train Penny to be the future ruler of there planet.

Doctor Smith uses the Space Pod to land on a planet that the Jupiter II is passing by. It turns out that the planet has evolved in such a way that plants are the highest form of life, and some of them are quite intelligent. One of these plants, a large carrot, captures Smith and tries to change him into a plant. The Jupiter II lands and the Robinsons and West come to Smith's rescue, only to be captured themselves. Eventually they thwart the plant creature and make their escape.

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.

Will returns to camp following a cosmic storm. John and Maureen are not there as they are at the weather relay station for a few nights. When he gets there, the rest of the family are acting strange. He finds out they are androids, sent to learn how to cope like the Robinsons and teach the rest of their race when they return home. The real Robinsons, are kept in a tube, as they are not allowed to come in to contact with thier double. Will must teach them to become like their counterparts.

When an alien believes that the Jupiter 2 has fired a missile at them that alien puts the crew in grave danger for there lives.

Poor Don West is sent to a prison camp.....WITH Dr. Smith! Don and Dr Smith are installing some equiptment, when Dr Smith comes across and alien prison escapee. The priosoner alien makes Dr Smith change jackets and then runs away. When the prison guards catch up with Dr Smith and Don, they arrest them for aiding an escape of a prisoner.

Before leaving their planet, the Robinsons meet a boy alien called J-5. They take him with them to return him to his home planet. They meet a strange ship, which turns out to be an earth ""lighthouse"" for lost ships. Thinking this ship will help them with extra fuel and star charts they celebrate, however when J-5 learns that they don't have enough fuel to take him home, he angrily sets about to destroy them all with a creation of his imagination. J-5 begins a new life at the lighthouse, and the Robinson's leave in the knowledge he will be looked after by the kindly, old lighthousekeeper.

The Jupiter 2 lands on a planet which serves as a junkyard. The Robinson's food supply is dwindling. So Dr. Smith tries to sell the robot and the ship in order to get food. Can Dr.Smith be stopped?

Penny meets up with Verda the Android Dr Smith ordered, who is on the run from a super android, IDAK. She is now much more human-like. IDAK however is faulty and is incapable of crushing anything or anyone. Another OMEGA-IDAK is released, and vows to ""crush, kill, destroy."" Verda hides with the Robinsons but out of fear she and Panny run, when Zumdish and his guard arrive to get her. IDAK is defeated, and Verda and the faulty IDAK take off together, obviously in love.

Alonzo P. Tucker returns, this time more in keeping with the pirate character he tried to create in his first appearance. This time Tucker is searching for Billy Bones' treasure, and is using the head of Billy Bones, which is kept in a box, to help him find it. He has three cutthroats with him, and he has to find the treasure and keep the cutthroats from endangering the Robinsons. Tucker's robotic bird is back again, and continues to torment the robot.

Dr. Smith and the Robot are exploring a cave. Smith pushes several buttons on a conspicuous control panel. The buttons activate a cyborg creating device. It up to Will to stop Dr. Smith.

Shortly after leaving their original crash-site planet, Smith spots a familiar star and, in an amazing show of stellar navigational skill, calculates the course to get back to Earth. He extracts a promise from Don and John that they'll return to Earth, or else he'll destroy his navigation data. They agree, but inform the family at dinnertime that they are headed for Alpha Centauri after all, mainly because the Earth is on the other side of the Sun (how do they know that? - do they know the date? And besides, from Alpha Centauri, Earth revolves clockwise, visible all the time). Smith changes course 180 degrees, then clumsily jettisons most of the fuel. They reach a refueling barge, one of several that Alpha Control put out in 1996, top up the tanks, and resume course for Alpha Centauri, not knowing that they've picked up a tailgater who follows them after Smith reverses course to Earth again. The alarm goes off in the night, and they expend a lot of fuel pulling away from the Earth's

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.