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.

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.

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.

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.

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.

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.

Actually, Will and Dr. Smith went into an elongated orbit and landed right back on the planet, not too far from the Jupiter II.

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.

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.

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.

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 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.

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.

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.

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 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.

Plants grow to huge proportions and can duplicate any item placed in them - but those items are made of plant material and are useless. John Robinson must use the biggest batch of plant killer he's ever mixed up to stop these things from engulfing the spaceship.

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.

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.

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.

The Robinson men discover an underground civilization while exploring the planet. Will wakes a sleeping princess who wants him to remain and rule with her.

The Intergalactic Delivery Service comes to Priplanus. Once again Dr. Smith seeks transportation and has Will "test drive" the spaceship. Will returns much smarter than when he left. Smith realizing the same could happen to him, the increase of intellect, boards the spaceship. His trip, however, ends in his rapid aging and subsequent impending death. To make matters worse, the owner of the spaceship has returned to take the vehicle back, stranding Will and Dr. Smith in their altered state.

Jimmy Hapgood lands on the planet and the Robinsons befriend him. After helping him fix his spaceship the Robinsons try to convince him to take Will and Penny back to Earth with him. Dr. Smith tries to get aboard the ship instead and take their place.

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.

The Robinsons meet a space traveler who turns out to be an Earth man, Alonzo P. Tucker, who was abducted from Punxsutawney, Pennsylvania, by aliens, in 1876. Tucker befriends Will by telling tall tales about being a pirate, but it turns out that he is only an ordinary man being pursued by aliens because he has stolen a mind reading device from them. Tucker returns the mind reading device to his alien pursuers, saving the Robinsons in the process.