List of ''Lost in Space'' episodes

In the year 1997, the Robinson family leaves Earth in the Gemini 12 space ship and sets out on a journey to be the first humans to colonize Alpha Centauri. Disaster strikes when their ship encounters a meteor storm, veers off course and crash lands on an alien planet. By December 2001, after a delayed revival from suspended animation, the family has settled in over a six-month period and made the planet their home, but a severe winter is coming and they must journey south. Traveling in their all-terrain "chariot," the family encounters fearsome cyclops monsters, survives a stormy sea, and explores the cave of an ancient civilization. Eventually they find a tropical region and set up camp, but unbeknownst to them they are being observed by a pair of humanoid aliens.
Guest stars: Don Forbes (TV Commentator), Ford Rainey (The President), Lamar Lundy (The Giant)

In the year 1997, the Robinson family leaves Earth in the Jupiter 2 space ship to colonize Alpha Centauri, but Dr. Zachary Smith (Jonathan Harris), working as a saboteur for a foreign government, rigs the environmental control robot to destroy the ship's control systems within hours after take off. Events lead to Smith being trapped aboard the doomed ship, which encounters a meteor storm and veers light years off course. Soon, the robot becomes active and does further damage before it can be stopped. Later, Professor John Robinson (Guy Williams) tries to fix the ship's sensor systems but must go outside the craft to perform the repairs. He becomes untethered and his wife Maureen goes out to help him.
Guest stars: Dick Tufeld (Voice of TV Commentator), Don Forbes (Second TV Commentator), Hal Torey (General), Byron Morrow (Lt. General Squires), Hoke Howell (Sgt. Rogers), Brett Parker (Security Guard), Ford Rainey (The President)

Maureen saves her husband and he makes the repairs to the ship, but an approaching comet heats the hull of the Jupiter 2 and the hatch door becomes stuck. Major West forces the door open and saves the couple. Next, the family finds a large alien ship which pulls the Jupiter 2 inside. The Professor and West explore the ship and try to figure out the craft's advanced navigation system in hopes of locating Earth. Meanwhile, young Will Robinson ventures onto the alien ship, followed by Dr. Smith. The two meet an alien creature and Will tries to communicate with it, but Smith hastily shoots with a laser gun. More aliens appear and the furious creatures chase everyone back to the Jupiter 2 which forces its way out of the alien ship to safety.
Guest stars: Dawson Palmer (Giant), Don Forbes (TV Commentator)

The family finds a planet able to support human life and the Professor feels they should land there. He decides to first check out the planet himself and goes off in a space suit with forearm mounted "Para-Jet" thrusters. The thrusters malfunction and contact is lost. Major West tries to land on the planet, but Dr. Smith demands they return to Earth and uses the reprogrammed robot to force his authority. West manages to subdue Smith but the Jupiter 2 falls from orbit and crashes on the planet. With everyone safe, West leads a mission in the chariot to find the Professor. Meanwhile, Smith schemes a plan to escape the planet and orders the robot to eliminate all "non-essential personnel."

The Robinsons begin to make themselves at home on the strange alien world, growing plants and herding local animals for food. After checking a meteorological station, the Professor learns that a severe cold front is coming which will drop temperature to lethal levels. To make matters worse, the Professor and Major West are attacked by a giant cyclops creature that lurks in the area. The family decides to abandon the Jupiter 2 and head south to a warmer climate, but Dr. Smith refuses to go with them. Journeying in the chariot, the family seeks shelter from a freak lightning storm inside a cave. There they find ruins of a past civilization in which to explore.
Guest star: Lamar Lundy (Giant)

The Robinsons continue their journey south where they encounter a frozen sea and drive across the ice. Back at the Jupiter 2, Dr. Smith deals with the severe cold, but just when he's about to freeze solid the temperature begins to swiftly rise. The robot computes that the planet is in a peculiar orbit around its star and will eventually become superheated. Now at risk of burning up, Smith sends the Robot to find and warn the Robinsons, but when it arrives, Major West shoots it with a laser thinking Smith sent it to harm them. West's hasty decision puts him at odds with the Professor and tempers flare along with the blazing heat wave. Heading back to the ship, the amphibious chariot must cross a now thawed and rough sea.

Will tries to raise Earth on the radio, but the signal is intercepted by a passing rocket ship that lands nearby. Appearing from the craft is a cowboy hat-wearing astronaut named Jimmy Hapgood. He explains he launched from Earth for Saturn in 1982, but veered off course when his guidance system failed and he has been lost in space ever since. Dr. Smith offers Hapgood the guidance system from the Robot as a gesture of good faith. Meanwhile, the Professor and Maureen make a critical decision – knowing Hapgood's capsule, Traveling Man, can carry two more passengers, they ask him to take Will and Penny off the dangerous planet and back with him to Earth. Hapgood refuses to accept the responsibility and Dr. Smith tries to weasel his way into the passenger seat.

Penny finds a cave where she is greeted by a curious voice that draws her inside to play. Later, she returns to the ship with stories of her new friend, "Mr. Nobody", who gave her shiny crystals as gifts. When Dr. Smith realizes the crystals are really diamonds, he tails Penny to the cave but is unable to get inside. He then tricks Major West into helping him blast the cavern open. Penny learns of the scheme and fears the blast could hurt her friend, but she is too late to warn him and is caught in a cave in when the explosives go off. Thinking Penny is dead, the formless entity threatens to punish those who have hurt her with a powerful wrath.
Guest star: William Bramley (Mr. Nobody)

Dr. Smith is beamed onto an alien ship that is bigger on the inside than on the outside. There, two mouth-less, floating heads tell him of their need for a replacement computer, but their technology requires the direct use of a human brain. After detecting treachery in Smith's mind, the aliens decide his brain is unreliable — much to Smith's relief — but they force him to provide them with another brain and fit him with a control collar which will kill him if he doesn't comply. To save his own neck, Smith decides to hand young Will over to the aliens and cons the boy into entering their ship. Meanwhile, the Robinsons come looking for their son and must save him before the aliens take him away.

An alien family, the Taurons, land on the Robinsons' planet and set up a camp nearby. Meanwhile, Dr. Smith is approached by the alien's scout robot, but he considers it an attack and thinks their new neighbors are hostile. Problems arise when attempts to communicate with the aliens becomes futile because they do not speak verbally. Later, Will encounters the alien's playful child, but the boy suddenly falls ill and Will takes him to a cave to rest. When the two boys do not return to their respective camps, the aliens and the Robinsons begin to suspect each other of foul play which could lead to a potentially deadly confrontation if the children are not found.

Major West is nearly killed when Dr. Smith causes an explosion, and a fed-up Professor thinks it best if he leaves. Dejected, Smith heads off, but he is followed by Will who feels sorry for him. Smith and Will then find the wreckage of an alien spaceship and a mysterious machine that creates anything they wish for. Word of the magical machine reaches the Robinsons who want to use the device as well, but their eventual greed forces the Professor to get rid of it. Refusing to destroy it, Smith takes it back to the alien ship, but there he summons a servant to tend to his needs. The machine instead conjures a menacing mummy-like creature who tries to take the machine away.

Major West and the Professor build a one-man space capsule in an attempt to reach help, but when Dr. Smith tampers with the ship, he and Will are accidentally launched into space. The two eventually land on a planet that Smith is convinced is Earth, but Will is not so certain. Will's fears are confirmed when they are captured by a strange plant monster that forces them to tend its garden. Meanwhile, the Robinsons pick up the capsule's signal and confirm it is still on their planet. West and the Professor begin a search to find the Doctor and the boy.

After a violent meteor shower, the women and Dr. Smith find the wreck of a spaceship, but whatever was aboard sneaks onto the Jupiter 2 and raids the food supply. Soon, a little dog makes an appearance, but Smith believes it a hostile alien in disguise. Meanwhile, a hairy creature spies the camp and the dog chases after it, but Smith believes the "alien" canine left to summon an invasion force. As Smith arms himself for war, Judy goes out to look for the dog unaware that the monster is tracking her down.

Penny, Will and Dr. Smith find an alien machine that beams Penny and her pet Bloop away, but Will manages to bring them back. Despite the Professor telling him to stay away from the machine, Will becomes obsessed with fixing it and has the Robot beam him to Earth. Will arrives in a small Vermont town and he tries to contact Alpha Control, but the locals who help him don't buy his stories of being from the Jupiter 2 mission. Back on the alien world (which Will calls "Priplanus"), the Robot stands by to bring Will back, but Dr. Smith reprograms him for another task which appears destined to strand Will on Earth.

Dr. Smith falls into a trance and walks into a glass cage where a monster comes and attacks him. A mysterious man suddenly appears and teleports the creature away. Later the man approaches the Robinsons and identifies himself as "The Keeper" — a collector of animal specimens from across the galaxy. It soon becomes clear that The Keeper plans to add the family to his exhibition when he asks Major West and Judy to come with him. Dr. Smith however, asks the alien for a ride to Earth where he can find all the humans he wants, but The Keeper has no interest and turns his sights on Will and Penny. Using the mesmerizing power of a strange staff, The Keeper tries to lure the children onto his spaceship and into cages.
Guest stars: Michael Rennie (Keeper), Wilbur Evans (Lighted Head)

Continuing the story from the last episode: Dr. Smith and the Robot sneak aboard The Keeper's ship where Smith tampers with the control systems and unwittingly releases a horde of monsters that escape onto the planet. Furious, The Keeper demands the Robinsons hand over Will and Penny, or he will let his creatures remain free to tear them apart. Both the Professor and Maureen, as well as Major West and Judy, offer themselves in their place, but The Keeper refuses them. Soon, The Keeper is injured during the escape of his most hideous monster and the Robinsons are left to deal with the beast themselves.

While the Professor and Major West investigate a landed alien ship, Will and Dr. Smith are captured by a pirate named Tucker and his mechanical parrot Nick. Smith has the Robot attack the pirate who runs off with Will as his prisoner. Will however, quickly befriends Tucker and becomes envious of the pirate life after hearing some of Tucker's exciting tales. Tucker makes Will his first mate and has him swear the pirate oath. Later, Tucker strikes a deal with the Robinsons to return Will unharmed if they help fix his broken ship. The Professor agrees, but soon another ship arrives and releases a blob creature that begins stalking Tucker for his treasure – a device that forecasts the future.

While drilling for fuel, Dr. Smith sets off an explosive in the wrong part of a bog and unleashes an invisible presence that begins prowling around. Later, Smith makes a ouija board and conducts a séance to contact his deceased Uncle Thaddeus. During the ceremony, the unseen force arrives and rampages around the Robinsons' camp leaving Smith believing it is the angry ghost of his uncle. When it is discovered that the entity can be trapped, and leaves behind three-toed footprints, the Professor and Major West believe it is something more real than supernatural – a dimensional creature that feeds off raw energy, and it is hungry for the Jupiter 2's vital power reserves.

Seeking shelter from a storm, Penny and Dr. Smith find a large mirror made of precious metal and Smith becomes obsessed with its potential value. After her pet bloop Debbie enters the mirror and returns with a bell, Penny tries the same trick but accidentally falls inside the mirror and into a pocket dimension. There, she meets a young boy who tells her that behind the mirror they can always have fun and stay as children forever. Penny, however, desperately tries to get out, and to make matters worse a hideous creature begins to stalk her. Outside, Dr. Smith tries to dismantle the mirror, not knowing he could trap Penny inside forever.
Guest star: Michael J. Pollard (Alien Boy)

Will is approached by a young boy named Quano who is from a race of disciplined warriors. He explains he has been put on the Robinsons' hostile planet to prove his bravery, because one day he will take his father's place as ruler of his people. As part of his test, he is to challenge someone to a contest of strength and skill and he picks Will as his opponent. Meanwhile, Dr. Smith eavesdrops on Quano and his father and learns that if Will beats him the father will cover up his humiliating failure by destroying any witnesses – i.e., the Robinsons. Smith then tries to strike a deal with Quano to ensure Will fails the contest in exchange for a ride back to Earth.

A freak storm destroys the Robinsons' garden and condenser unit, forcing the family to ration protein pills. Dr. Smith and Will soon find a series of alien advertising signs which lead them and to an outdoor bazaar run by a space trader. The trader shows them incredible wares and tasty food from around the galaxy, but the greedy businessman's prices are too high for the Robinsons who require every vital piece of equipment they have. Dr. Smith, on the other hand, is willing to trade anything for a decent meal, including the Robot. Learning of the unauthorized sale, the Professor orders Smith to get the Robot back, and in doing so, the trader tricks the doctor into signing himself over as a slave. When the Robinsons learn the merchant has a weather-controlling machine, they realize they have been swindled and try to get Dr. Smith back.

Will finds a golden crown and, putting it on, he summons an entourage of people who hail him as the new king of the planet Andronica. The aliens explain they leave a crown out in the open whenever they need a new leader and whoever finds it gets the job. Believing the position is too much for a boy, Smith convinces Will to surrender the crown to him. Smith gets the royal treatment but soon discovers his subjects are androids under the control of a mad scientist who plans to sacrifice Smith and rid the galaxy of a useless being. In the meantime, the man makes a good-natured clone of Smith whose kindness and hard work causes the Robinsons to suspect something isn't right and the real Smith must be in grave danger.

Will and Dr. Smith are attacked by a werewolf and they set out to track the beast down. The footprints lead them to a family of hillbilly farmers who seem to worship the strange plants they raise. A feud begins to brew when the Robinsons learn the aliens are stealing equipment, and Judy becomes jealous when the farmer's daughter Effra flirts with Don. Meanwhile, Smith is charmed by the mother, Sybilla, and proposes to her, but only to weasel a ride back to Earth. Soon however, Smith becomes horrified when he learns Sybilla and her daughter are witches and his future stepson Keel becomes a hairy beast under a full moon.

Penny encounters an interstellar fugitive named Ohan whom she helps, and he gives her a talking disc that leads to a great treasure. Soon a galactic law man named Bolix arrives looking for Ohan, but the disc is what he's really after. Smith learns of the disc and follows it to the treasure – a box containing a metal collar that turns anything he touches into pure platinum. Smith's midas touch quickly becomes a curse when the collar won't come off and he accidentally turns Penny into a platinum statue.

During a search for water, the Professor, Major West, Will and the Robot find the remains of an ancient city deep inside a cave. Soon an earthquake hits, and Will and the Robot fall down a pit that leads to an underground world. The Professor and West try to rescue them, but they are captured by a group of soldiers and brought before their leader. Meanwhile, Will finds a little sleeping princess and he awakens her with a kiss. Once awake, she tells Will that he will fulfill a thousand-year-old prophecy where he becomes her husband and she leads an invasion army that will take over the universe – starting with planet Earth.

Will and Dr. Smith find a strange alien spaceship that the Robot states is capable of traveling anywhere in the universe. Later, Will goes inside the craft, but the hatch closes and the ship takes him on a wild ride into the sixth dimension. Mutated by exposure to the cosmic forces, Will returns with super-human intelligence. Hoping a ride in the ship will give him similar mental prowess, Smith takes off next, but he instead returns a fragile old man and blames Will for his predicament. Will then uses his advanced intellect to find a way to revert Smith's condition, but soon a scaly alien arrives angry that his ship has been tampered with.

While exploring a cave containing ancient artifacts, the Professor finds a tomb and encounters a ghostly entity named Canto who slowly possesses his mind. When he returns to the ship, he exhibits hostility and fatigue which Dr. Smith believes is the beginning of a mental breakdown. Meanwhile, the entity gives the Professor the technical knowledge to repair the Jupiter 2 so it can leave the planet. Once the family learns their father may be under the influence of an alien, they try to stop him, but time is running out as the being's control over their father grows stronger.
Guest star: Gregory Morton (Alien Voice)

Dr. Smith and Will encounter an intergalactic prospector named Nerim who is mining for Cosmonium, a substance he claims is the most valuable material in the universe and that it contains the force of life. Unfortunately, Nerim's subterranean blasting has caused the core of the planet to become unstable and the Robinsons rush to get the Jupiter 2 ready for departure. Meanwhile, Smith plays Nerim in a card game and gambles for some of the Cosmonium, but instead he ends up losing a vital component for the Jupiter 2 which could hinder the Robinsons' escape.

Claiming he has found the way to Earth, Dr. Smith tampers with the navigation controls and inadvertently dumps all the Jupiter 2's reserve fuel supply. Hope is shattered when the Professor locates an Earth fuel barge but the tanks are found nearly empty. Meanwhile, Smith begins to see a beautiful, green-skinned woman floating outside the viewports who sings his name, but no one believes his wild story until the girl lures him outside the ship. With the little fuel they have squeezed from the barge, the family is forced to make the decision to save Dr. Smith and miss their chance of returning to Earth.

The Jupiter 2 is pulled down to a strange planet that Dr. Smith believes is Earth. Soon, a friendly voice makes contact and identifies itself as "Space Control", but the Robinsons are suspicious. After landing, they send the Robot out to investigate, but Smith impatiently tries to make contact himself. Expecting a big welcome party, Smith instead is approached by a group of androids and their robot leader who demands he surrender all weapons and offers a treasure if he complies. Driven by greed, Smith steals the Robinsons' weapons and hands them over, but the robot tricks him and forces him to work on a laborious assembly line.

After evading an alien missile, the Jupiter 2 suffers damage and the Robinsons are once again forced down on an unknown world. Dr. Smith sends the Robot out to investigate the mist-shrouded planet and when it doesn't return, the Professor forces Smith to go out and search for it with Will sneaking out to join him. After finding the Robot, Smith and Will encounter a hostile, reclusive hermit named Tiabo, who pretends to be part of an alien army in hopes of frightening the Robinsons away. Meanwhile, Smith becomes a human bomb when he consumes what he thinks is an exquisite drink, only to learn it was an explosive liquid.

Dr. Smith, Will and Penny encounter a charismatic entertainer named Dr. Marvello who operates an intergalactic circus. Although dismayed to learn that there are only the seven castaways to entertain, Marvello puts on a show anyway. Hoping the troupe will swing by Earth, Smith tries to join them with a song and dance routine, but the ringleader's interest is in young Will who exhibits amazing powers of conjuration. Marvello then offers Smith the job of being Will's manager if he can coax the boy into joining the show.

An alien from a galactic tribunal appears at the Robinsons' camp carrying a talking computer that accuses the family of committing crimes in space – namely their previous trespassing aboard an alien ship and leaving junk in space when the Professor lost tools while repairing the Jupiter 2. The aliens hold the family behind an energy containment wall and then summon them one at a time to give their testimony of what really happened. The aliens soon realize Dr. Smith is the only guilty one who caused the problems and threaten to imprison him. The Robinsons, however, sign a petition to excuse Smith by reason of insanity.

Dr. Smith finds an alien vending machine and unintentionally orders a servant android named Verda. Smith however, becomes annoyed with the android and passes her off to Will and Penny to befriend. Soon, a celestial department store manager named Mr. Zumdish arrives and notifies Smith that the payment for Verda is past due, but Smith refuses to pay claiming Verda is defective merchandise. Zumdish demands Verda back, but the Robinsons refuse to hand her over believing she has developed human feelings and is no longer a piece of merchandise.

After Professor Robinson defeats a gladiatorial brute in hand-to-hand combat, he is approached by an intergalactic fight promoter who requests he enter his games. The Professor refuses, but after Dr. Smith learns a fighter could stand to earn riches beyond imagination if they win, he tries to enter the games himself – but only after cutting a deal to face what he believes is the weakest opponent. Meanwhile, Major West and the Professor eavesdrop on the promoter and learn that if Smith should lose the match, he dooms Earth to alien invasion.

Will and Dr. Smith are attacked by an Arabian thief and they run back to the safety of the Jupiter 2. No one, however, believes the story of their encounter, especially Penny – that is until she, Will and Smith are whisked away in a spaceship sedan chair to a nearby asteroid where the thief has set up his camp. Penny is put to work tending a furnace while the thief recruits Will to help him find his lost love – a princess he believes is trapped somewhere back on the Robinsons' planet. Meanwhile, Smith is mistaken as the return of the cruel vizier who imprisoned the princess and the thief vows revenge against him.

Dr. Smith flees in terror when his estranged cousin, Colonel Jeremiah Smith, has tracked him down and pays him a visit. Although the Robinsons show Jeremiah hospitality, Dr. Smith adamantly refuses to see his relative. Everyone thinks Dr. Smith is being rude, until they learn that the cousin is trying to kill him because the last surviving member of the Smith family will get their late Aunt Maude's fortune. The Professor forces the two cousins to a truce, but Jeremiah cons Dr. Smith into gambling away the inheritance on a robotic slot machine. The scheme backfires, however, when the machine tries to kill one of them for the payment.

Dr. Smith is accosted by an interstellar gunslinger named Zeno, who happens to be his mirror-double. Zeno forces Smith to swap clothes and has him arrested by a galactic lawman. While Zeno hides out among the Robinsons, Smith is taken to another planet to stand trial and Will is brought along as a material witness. Once at the planet, Smith and Will manage to escape the lawman and find a town full of residents who fear the real Zeno, and Smith takes advantage of the mistaken identity. When another gunslinger arrives to challenge Zeno, however, Smith's cowardice blows his cover. Fleeing back to the Robinsons' planet, Smith returns with the lawman right behind him, but a problem arises when no one can tell Zeno and Dr. Smith apart.

When Dr. Smith finds a golden harp, he strums it and transports himself to a hell-like place filled with fire and brimstone. There, a devilish man named Morbus presents a review of Smith's devious life and promises eternal damnation if he doesn't change his ways. Morbus lets the terrified Smith go, but only if he agrees to destroy the harp. Smith is happy to do so, but his attempt ends up releasing Morbus from his fiery dimension. Once free, Morbus meets Judy and quickly takes a liking to her which annoys Major West. Meanwhile, Smith learns Morbus isn't the Devil, but an alien, and the dimension is a prison that the harp provides access to. Smith tries to return Morbus back to the prison, but in doing so he unwittingly sends Judy there as well. West then threatens to rip Smith's head off if he doesn't figure out how to get Judy back.

Dr. Smith, Will and the Robot find a cave where they encounter shadowy beings who demand the Robot be given to them to examine. The three flee back to the Jupiter 2 where aliens project a message to Professor Robinson with an offer to buy the Robot, but he refuses to sell. When the aliens threaten to harm the family, the Robot voluntarily gives himself up for their experiment. The beings end up taking the Robot apart and then later dump his parts in a heap on the Robinsons' doorstep. Will rebuilds the Robot, but suddenly everything mechanical around the ship goes haywire. The Robot warns that the aliens are building a weapon that controls machinery and the Robinsons must stop their evil plans.

Penny encounters an android named Raddion and its creator, Sesmar, who is intrigued with her feelings for beauty and compassion and wishes to instill such qualities upon his machine. Sesmar tests the Robinsons' feelings with a special camera he gives Dr. Smith, and then tricks the family into entering his lab where he drains the emotions from their minds and leaves them irritable and lazy people. Major West, who refused to participate in the experiment, has to team up with his nemesis Dr. Smith to stop the mad scientist and return the Robinsons to normal.

While the men are off exploring the planet, the women and Dr. Smith are approached by a handsome golden-skinned man named Keema, who offers them extravagant gifts and friendship. Keema explains he is at war with a belligerent and hostile, frog-headed alien that Penny and Dr. Smith had encountered earlier. Despite Keema's hospitality, Penny distrusts him and goes to talk to the frog. She finds the creature a more likable being who simply wishes to survive and fights only to preserve his people. Meanwhile, the golden man asks Smith for the Robinsons' weapons, and in return he offers Smith a lift back to Earth. Smith foolishly gives the man the weapons, and the alien reveals its true form – a twisted-faced monster who really plans to destroy the Robinsons once he finishes off his enemy.

The green space girl Athena – who hypnotized Dr. Smith while the Jupiter 2 traveled through space – returns when Smith finds her with a dimensional telescope. While Athena showers affection upon Smith, a former suitor of hers, Urso, arrives and challenges Smith to a duel. To make sure Smith accepts the challenge, Urso curses innocent Will with green skin and hair. Meanwhile the telescope begins to show glimpses of the future, and Smith becomes terrified when he sees what he believes is his own funeral.

Dr. Smith and Will encounter a bumbling knight named Sagramonte who is on a great quest to slay a beast called Gundemar. He has been chasing the beast for 40 years across many worlds and Will admires him for his bravery and tries to help him in his quest. Meanwhile, Smith tries to find the Knight's ship in hopes he can get back to Earth, until he learns the Knight travels via magic he does not understand. Later, Penny encounters Gundemar and finds the beast a kind being who she quickly befriends and tries to hide from the horrible knight.

Dr. Smith and Will find another alien vending machine, but this one appears broken. Again, Smith fiddles with the controls, but he disappears into the machine. Will tries to get him, but he too is teleported away. Will finds himself in a toymaker's shop where he meets Mr. O.M., who thinks Will and Smith are escaped toys and sends a windup monster after them. Outside the machine, the Professor and Major West try to get Will and Smith back, but the machine's owner, Mr. Zumdish of the Celestial Department Store, returns and declares the machine "outdated" and must be destroyed.

Dr. Smith conducts a rain making experiment, but his device malfunctions and destroys a vital piece of equipment. Fed up with his mischief, Professor Robinson exiles him. While away, Smith finds a crashed spaceship and announces to the Robinsons that he will fix the craft and leave them behind. Smith's plan backfires when he and Will encounter the ship's owner – a mad space admiral named Zahrt who forces Will, Smith and the Robot to repair and crew his vessel. After stealing a propulsion unit from the Robinsons, Zhart blasts off to seek revenge against his former mutinous crew who stranded him on the planet.

While reciting lines for a play, Dr. Smith summons a pair of magical gloves and the golden hammer of Thor. Smith then encounters Thor's wife Brynhilda, who takes him to Valhalla upon a winged horse. Soon, Will arrives with Thor who has been searching for the gloves and hammer, but Brynhilda claims the hammer has chosen Smith to replace Thor as the warrior deity. Infuriated, Thor challenges Smith to a duel to the death. Terrified that he will be killed, Smith tries to use psychology on Thor, who breaks down admitting that he feels washed up and is unable to fight again. Now Will and Smith must give Thor his confidence back when a group of Titans arrive and threaten to destroy his kingdom.

Dr. Smith thinks he is going mad when he encounters a magician named Zalto who only he can see. The Robot, however, confirms the Magician's presence and leads Smith and Will to his secret lair. There, Smith learns Zalto has his own spaceship and the wizard plans to promote himself by using the craft to destroy an asteroid with the resulting explosion spelling his name among the stars. Smith volunteers to be Zalto's apprentice so he can swindle his way aboard the ship and take it back to Earth. When Smith boards the craft, Zalto pushes Will inside with him and launches the ship. As planned, Smith goes to Earth, but thinking they are hostile aliens, Earth defense launches missiles at them.

While the Robinsons prepare the Jupiter 2 for lift off, Dr. Smith has an accident and suffers amnesia. He is then lured to a cave where he finds an ancient computer that manifests anything he desires. When Will fetches Smith for take off, he finds him physically transformed into a silver-skinned being named Oniak whose mind is being filled with alien knowledge. Later, the Professor and Major West try to convince Smith to return, but they find him completely taken over by the alien presence who refuses to leave the planet. With minutes before lift off, the Robinsons give up hope of returning Smith, but Will sneaks away determined to bring him back.

Captain Tucker the space pirate returns in search of a mechanical head-in-a-box that thinks Dr. Smith is its former master – the late pirate "Billy Bones". Hot on the trail of Bones' treasure, Tucker lies in wait for the head to reveal the location to Smith. Tucker's impatient crew, however, wants the treasure now and forces Smith to lead them to it, but the head doesn't cooperate and puts Smith's life in danger. Meanwhile, Will, who admired Tucker, becomes disappointed when he learns he has taken up with bad company again when he promised to lead an honest living the last time they met.

While Dr. Smith, Will and the Robot chase after a ruby-eating creature, they encounter a super-android who identifies himself as IDAK (Instant Destroyer and Killer) and walks around shouting "Crush! Kill! Destroy!". Thinking the machine could be useful to him, Smith tries to draw up a service contract. Meanwhile, the female android Verda returns to the Robinsons after escaping a disassembly order, and she warns them of the android that was sent to destroy her. When IDAK detects Verda's presence, he goes after her, but the family is determined to save Verda by playing off the destroyer's human emotions. Unbeknownst to everyone, a second IDAK – one stronger and unsusceptible to human feelings – is sent to replace the flawed IDAK.

While the Robinsons set up an array of radio dishes, a harsh feedback noise sounds though the system and fries all communications. A woman's voice, that orders them to surrender, is the only thing they can hear. The Robinson children and the Robot are then taken prisoner by alien guards while the adults are approached by a warrior woman named Niolani who has the men taken as slaves. Niolani has the men build her a transport arch so that her people can come to the world and colonize it as part of her female-dominated empire. Meanwhile, Will and Robot come up with a plan to sabotage the arch so everyone can escape.

While the Professor and his wife are off exploring, the Jupiter 2 camp comes under attack by an alien force. Will tries to get a message through to his parents at a relay station, but when he returns to the ship, he finds Dr. Smith, Major West, Penny and Judy acting strangely and the Robot damaged. Will then finds a cave and encounters an alien named Lemnoc who has created android duplicates of the family while the real members have been put into stasis. Will demands their release, but Lemnoc wants him to teach his androids to act as humans. Will agrees to help, but Lemnoc has a devious plan for his androids to steal the Jupiter 2.

Dr. Smith causes another accident, and once again the Professor banishes him from the camp. While spending the night in the wilderness, Smith is accosted by dozens of tiny robots who hold him prisoner. The mechanical men then approach the Robinsons and demand their Robot come to them to be their great leader. The Robot complies, but the sinister mechanical men find him too kind and tolerant for their needs. Preferring Smith's treachery and ruthlessness, they transfer Smith's personality to the Robot's body and vice versa. Now Smith-minded Robot commands an unstoppable mechanical army on a mission to seize the Jupiter 2 from the Robinsons, while the Robot-minded Dr. Smith feels he is obligated to stop them himself.

Seeking shelter from a storm, Will and Dr. Smith enter a cave, but the opening collapses and traps them inside. Searching for a way out, Will finds a revolving door which leads to a Scottish castle back on Earth. There, Will is chased by a terrifying monster and later encounters a mischievous ghost named Hamish who follows Will back to the Robinsons' planet where he appears in the flesh. The Robinsons reopen the portal for him and Dr. Smith volunteers to go through as well to contact Alpha Control, but his stay on Earth is short once Hamish learns an ancestor of Smith was responsible for his ghostly curse and he tries to enact revenge upon him.

While Dr. Smith, Penny and Will conduct a play, a sickly alien named Arcon appears and begs for help. Penny takes him back to the Jupiter 2 to rest, but soon a trio of aliens called the Saticons appear and demand Arcon surrender to them. Penny refuses to betray her new friend and the Saticons turn down the heat in an attempt to freeze the Robinsons to death. Arcon decides to leave, but he gives Penny his magic belt for safekeeping. Smith then goes to the Saticons to inform them that Arcon has left, but the aliens know Penny has the belt and offer Smith the use of their molecular transporter to beam himself back to Earth if he gets it for them. Smith schemes to hand off a forgery of the belt instead, but unbeknownst to him, the aliens really plan to transport him to a duplicate of San Francisco's Chinatown on a lifeless asteroid.

A comet threatens to impact the Robinson's planet and the family is forced to make a hasty escape in the Jupiter 2. Once in flight, Dr. Smith fools with the airlock controls and accidentally sends The Robot into space. Next, the Jupiter 2 docks with an alien spaceship and the Professor and Major West venture inside and reunite with the Robot. They soon realize the ship is an automated prison filled with alien felons in suspended animation. Once again, Smith tampers with controls he doesn't understand and releases a dangerous prisoner who tries to free the other inmates and take over the ship.

The Jupiter 2 is caught in a space warp and accelerates on a wild ride. Once it's over, the Robinsons are shocked to see planet Earth lingering before them. There is no contact with Alpha Control, but the Professor decides to land anyway and sets the ship down in a small Michigan town which they find strangely deserted. Turning on a radio, the Professor learns they have time warped to the year 1947 and the townsfolk think they have been invaded by aliens. Meanwhile, Dr. Smith believes he can make a fortune advancing the technology of the backward era and, disguised as a fire chief, he tries to lead a vigilante force to take the Robinsons prisoner.

Dr. Smith intercepts a distress call from an alien ship that asks for medical assistance and promising a "great reward" to whoever helps. Smith and the Robot take the space pod and board the alien craft where they find a crew of androids who take Smith to their sick leader – a malfunctioning computerized brain. Smith realizes he is in over his head and tries to leave, but the androids threaten to kill him if he backs out. The Robot comes to the rescue stating he can fix the computer, but he refuses once he learns the brain is evil and wants to take over the universe. Meanwhile, the androids capture the Jupiter 2 and threaten to kill the Robinsons if the Robot doesn't conduct the repairs.

Professor Robinson and the Robot head out in the space pod to investigate a nearby planet. After landing, the Professor kills a hostile creature and he is quickly approached by a furious alien named Megazor who claims he has cost him points in an intergalactic hunt by killing the beast. The alien hunter then decides the Professor will make a more valuable target and has him prepare himself to survive as the target for the next hunt. Back on the Jupiter 2, Dr. Smith refuses to risk a rescue of the Professor and tries to force the ship back to Earth. He instead fouls the controls and causes a crash landing. Once again, the Robinson family is stranded on an alien world.

While the Jupiter 2 is threatened by lava flows from an erupting volcano, Major West and a reluctant Dr. Smith are on a mission in the chariot to cap the mountain with a nuclear explosive. Arriving at the site, the two are accosted by a tribe of cavemen who worship an ancient computer that gives the chief strange powers. West tries to warn them of the danger the volcano poses, but the chief has him and Smith sealed up inside a cave. As the oxygen runs out, Smith and West try to reconcile their differences as the end draws near. Meanwhile, the Professor, Will and the Robot mount a rescue, with the Robot challenging the computer as the mechanical leader of the tribe.

After Dr. Smith, Will and the Robot find a cave full of strange machinery, Smith fiddles with the controls and creates a faceless android that chases him back to the ship. The Professor destroys the android and has Smith confined to his quarters, but he later sneaks back to the cave to make more androids. This time, however, they are not only programmed to serve Smith, but look just like him. When Will learns of Smith's personal army, he tries to stop him, but Will becomes trapped in the android machine and emerges as a Smith-faced android programmed with the twisted desire to control the universe.

Moments before takeoff, Penny encounters an elf-like boy named J-5 who claims to be the last survivor of a doomed colony, and the Robinsons take him with them when they leave. Soon the Jupiter 2 comes upon a remote Earth space station commanded by an eccentric old man, Colonel Fogey, who offers the Robinsons enough fuel to get back to Earth. Unfortunately, he doesn't have enough for them to swing by J-5's world as well. Upset that he won't be going home, J-5 unleashes his imaginary friend Zaybo upon the station and tries to steal the Jupiter 2.

Dr. Smith, Will and the Robot are accidentally launched away in the space pod and land on a nearby planet. The family chases after them but crash lands nearby in a barren desert. Meanwhile, the pod crew find themselves in a tropical rainforest even though they are a half-mile from the ship. Feeling sleepy, Smith and Will take a nap, but wake up over 270 years in the future where Will meets a distant relative that looks like Judy. Likewise, Smith meets a great-great-great grandson who blames him for tarnishing the Smith family name.

A group of spaced-out hippies arrive on the Robinsons' planet and begin setting up planetary explosives. They claim the planet is on a collision course with their world and they have been tasked to destroy it, leaving the Robinsons little choice but to rush repairs and get the Jupiter 2 back into space. In the meantime, Dr. Smith is exposed to a strange gas and passes out. He later awakens with curly green hair and superhuman strength.

The Jupiter 2 is caught in the orbit of a fog-shrouded planet where a gaseous entity creeps aboard. When it learns Will "just wants to be alone," people begin to disappear, starting with Maureen, Judy and Penny, then Major West and Dr. Smith. Finally the Professor and the Robot vanish and Will finds himself completely alone and terrified. Meanwhile, the others find themselves in a foggy realm and tormented by an evil entity who feeds off their fear.

The Robinsons land on a planet and are followed down by a space capsule that crashes nearby. Soon, two androids arrive with orders to take the capsule, but they believe the Robinsons are hiding it and attack them. Meanwhile, the Robot locates the capsule and encounters a female robot. Although she is evil, the Robot begins to fall in love and is easily manipulated to serve her. When she demands a device the Robinsons cannot live without, the Robot's loyalties are tested.

Penny encounters a caveboy named Oggo who tries to warn her of an evil zookeeper named Farnum, but she is captured in Farnum's trap and he adds her to his collection of human exhibits. Later Farnum captures Major West and Judy, then Dr. Smith and Will. While Will, Penny and Oggo try to escape, Will and Farnum are knocked through a portal and become trapped on a hostile planet. With Farnum out of the way, Dr. Smith tries to take over the show once he learns how lucrative a space zoo can be.

A group of alien bank robbers, disguised as humans, brainwash the Celestial Department Store manager Mr. Zumdish into thinking he is a galactic tour guide. With the thieves looking for a place to lie low, Zumdish contacts Dr. Smith who learns the "vacationers" are willing to spend lots of money for some R & R. With the rest of Robinsons off on a survey mission, Smith turns the empty Jupiter 2 into a 5-star resort with Will as the bellboy and the Robot laboriously filling every other position a hotel needs.

Major West, Judy, Will, Dr. Smith and the Robot are on a mission to install a radar station when Smith stumbles upon a being frozen in a block of ice. While standing guard, Smith carelessly places a thermal blanket over the ice and it melts releasing an alien princess. Soon, a silver-skinned bounty hunter-desperado named Chavo arrives and holds Will captive under the guard of fake soldiers. Chavo then demands West surrender the ice woman or he will harm the boy. West challenges Chavo to a duel to save to her instead.

While in space, Dr. Smith separates the Robot's upper body from his track section which wheels itself into the space pod and takes off. The Robinsons chase the pod to a nearby planet where it lands amidst an alien city. There, the family encounters a race of blob creatures that all look the same. Wanting to experience human individuality, the aliens take the form of the Robinsons and hijack the Jupiter 2 on a course for Earth. Will and Smith, having sneaked aboard, try to sabotage the ship and warn Earth that the ship has been taken over by hostile aliens.

On a search to find a missing Princess, a space captain named Kraspo believes Penny is the girl he is looking for. Will tries to convince the captain that he's made a mistake, but Penny passes all his tests to verify her identity including feeling a pea hidden under a mattress. Once Dr. Smith learns he could live like royalty serving Penny in her kingdom, he tries to convince the bewildered girl to accept the situation. Meanwhile, Will overhears Kraspo's robotic crew plotting a mutiny to take over during Penny's coronation ceremony.

While conducting an experiment to capture cosmic energy, Will inadvertently traps Chronos, an alien who controls time. Furious at Will for interfering in his business, Chronos forces the boy to return with him to his factory. When Professor Robinson learns what happened, he and the Robot pursue the alien, followed by Dr. Smith. When Smith learns Chronos' machine can transport him through space as well as time, he "steals" a ride back to Earth in 1997, hours before the launch of the Jupiter 2. Chronos warns Robinson that unless Dr. Smith is on board the Jupiter 2 at lift off, the ship will eventually be destroyed by an uncharted asteroid and the Robinsons and Major West will all be killed.

The Robinsons finally arrive at their destination, the Alpha Centauri system, but they are surprised to find an Earth colony already established there. Another oddity is that it only seems to be populated by teenagers who try to brainwash Penny and Will into rebelling against the "olders." When Dr. Smith snoops around, he discovers the teens are really aliens in human guise, but they give Smith his youth back and make him forget what he saw. The aliens, who never grow older-minded than adolescents, try to discover what makes the human children mature.

Major West and Dr. Smith encounter an alien fugitive who forcibly swaps his prison shirt for Smith's jacket and flees the scene just as prison guards arrive. West and Smith then find themselves accused of aiding the criminal and stand trial before a computerized judge. Will and the Robot act as their legal council, but the two are found guilty as charged and sent to the notorious prison planet Destructon to serve life sentences. There the two overhear another prisoner's escape plan and Smith is willing to go along with it. West, however, holds on to hope that Will and Robot can somehow arrange a legal release.

The space traveling showman Farnum B. returns seeking contestants for a Miss Galaxy pageant and sets his sights on Judy when his mysterious sponsor demands she enter. Judy turns down the offer, but Dr. Smith, knowing he could profit greatly for signing her up, coerces her into signing a contract. When Major West reads the fine-print he learns the winner of the contest must be given over to the sinister being who is made of fire and comes from a dark world without beauty.

The Jupiter 2 passes through a radiation storm and Dr. Smith's alien plant mutates, growing into an intelligent monster. He dumps it out the airlock, but it attaches to the hull and endangers the ship. The Professor takes the ship into a planet's atmosphere to burn it off the hull, but the inhabitant of the world attacks and drains the ship's energy. Stuck in orbit, Major West forces Smith to go with him down to the planet to talk to the attacker – an alien called the Sobram. The being offers to spare the Jupiter 2 only if the Robot stays behind and plays a wargame with him. Unbeknown to all, the plant creature has made it to the surface and begins to multiply into an army of its own – and becomes a far better challenge for the Sobram.

As the Robinsons celebrate the Robot's birthday, Dr. Smith sneaks off in the space pod to a planet dominated by plants. After pulling a flower, he is accused of murder by Tybo, a carrot-man, who punishes him to an eternity of literal tree-hugging. The family lands to search for Smith and meets a purple-haired botanist named Willoughby who explains that Tybo is the one in charge. After Smith is transformed into a talking stalk of celery, and Penny grows into a flower bed, the Professor and Major West try sabotaging Tybo's moisture-control system to stop the plant tyrant.

A fire breaks out aboard the Jupiter 2 and the Robinsons must land on a nearby planet to make repairs. They momentarily lose contact with the Robot, who has taken the space pod to scout ahead. Upon landing, the family discovers the entire planet is a massive junkyard run by a strange metallic junkman who has no intention of letting the Robinsons leave. When the ship's food supply becomes contaminated by a "rust blight," Dr. Smith bargains with the junkman for food, offering parts from the Robot to replace the junkman's own degrading circuits. The junkman eventually sets his sights on Jupiter 2, and after upgrading himself with the Robot's parts, he steals the ship with Dr. Smith aboard and leaves the Robinsons behind. Will follows in the space pod hoping the Robot's memory banks, now part of the junkman, can influence a change of heart.