The first season of Lost In Space is widely regarded by fans as the best, with the first 5 often mentioned as the finest episodes of the show.
Earth’s first family in space faces trials and tribulations as they become lost on their way to colonize a planet circling Alpha Centauri. Smith and the Robot are noticeably absent.
A saboteur reprograms the Robot to destroy the Jupiter 2, but gets trapped aboard at launch. The Jupiter 2 is damaged, but survives and becomes hopelessly lost in space.
The crew of the Jupiter 2 encounters a seemingly derelict space ship that dwarfs the Jupiter 2.
Professor Robinson attempts to scout a desolate planet, but his parajet rockets fail. Major West attempts to land on the planet to search for the Professor, but the Jupiter 2’s rockets also fail and the ship crash lands.
The Jupiter 2 crew faces dangers on the planet they crashed on, including a gigantic cyclops, microbes in the soil that cause crops to grow out of control, and an erratic orbit that causes extreme heat and cold.
The Robinsons and Major West head south in the Chariot to avoid the incredibly harsh cold. Meanwhile, Smith discovers that the erratic orbit of the planet around its sun will cause a sudden and intense temperature spike and sends the Robot out to warn them.
A fellow space traveler from Earth, Jimmy Hapgood, happens to land on the planet where the Robinsons are stranded. They help him repair his ship and John and Maureen ask Jimmy to take Will and Penny back to Earth. Smith, however, has other plans.
Penny makes friends with a mysterious invisible entity in a cave. It talks to and learns from her. But Dr. Smith draws the wrath of the entity when he destroys the cave in search of riches and, in the process, inadvertently injures Penny.
Invaders From The Fifth Dimension, in the form of floating alien heads, search Preplanis for a humanoid brain to power their spaceship and take them home. When they capture Smith, they quickly find out that he’s, by Smith’s own admission, “a scoundrel, a thoroughly bad sort, hopelessly unreliable”. So, Smith offers up a “small Robinson”, one that will fit in the alien ship… Will.
When Smith uses all of the potable water for a shower, he forces the Robinsons to search for a new water source. They find it, in the form of fruit that grows in a brackish well. Unfortunately for Smith, he eats it before Professor Robinson has a chance to test it. Smith runs off, sure the Robinsons have purposely poisoned him, and takes the last of the working fuel cells with him. Unbeknownst to him, he turns into a paranoid giant overnight.
An alien probe precedes the arrival of an alien race of beings called the Taurons. The Robinsons believe these aliens are peaceful and looking to settle on Priplanus. Dr. Smith, however, thinks they are the first arrivals of an enormous invading army.
Smith and Will stumble on to a derelict alien ship and discover a machine that grants wishes. Use of the machine causes tensions in the group.
Will’s attempts to build a probe to get a message back to Earth fail and leave the deutronium supply seriously depleted. Don and John’s then develop an alternative fuel, but can’t stabilize the output. The decision is made to pull the reactor chamber out of the Jupiter 2 and turn it into a small craft with which Don will attempt to find rescuers. Smith, however, has other plans.
While Don, John, and Will are away from camp, an alien intruder invades the camp to steal food. While investigating the incident, Mrs. Robinson, Judy, and Penny discover a wrecked space capsule and the dog that had ridden in it. Dr. Smith thinks the dog is a spy.
After being exiled from camp, Dr. Smith discovers plants that can duplicate anything and feed off deutronium. Judy ends up being cloned and only Dr. Smith knows it’s not her.
When Will discovers a matter transfer machine left behind by the Taurons, he takes a trip back to Earth. He arrives in Hatfield Four Corners, Vermont. While there, he tries to contact Alpha Control to make them aware of the Robinson family’s fate, but no one believes him.
An alien animal keeper travels the universe looking for unique specimens to add to his menagerie. When he comes upon the Robinsons, he’s determined to add a pair of humans to his “zoo”.
Dr. Smith angers the Keeper by accidentally releasing all his animals. The Keeper demands Will and Penny as recompense for his losses.
While the Professor and Major West investigate an alien ship, Will and Dr. Smith are captured by the pirate Tucker and his mechanical parrot. Will befriends Tucker and becomes his first mate after hearing thrilling pirate stories. Tucker agrees to return Will if the Robinsons help fix his ship. However, a bloblike creature from another ship begins stalking Tucker, seeking his treasure—a device that predicts the future.
While drilling for fuel, Dr. Smith accidentally sets off an explosive in the wrong part of a bog, releasing an invisible entity that begins lurking nearby. Later, Smith uses a ouija board to hold a séance, attempting to contact his deceased Uncle Thaddeus. During the séance, the unseen force rampages through the Robinsons’ camp, leading Smith to believe it’s his uncle’s angry spirit. However, when the entity is trapped and three-toed footprints are found, the Professor and Major West suspect it’s not supernatural, but a dimensional creature that feeds on raw energy—and it’s after the Jupiter 2’s power reserves.
Will and the Robot discover a more advanced alien robot. This new robot quickly gains the Robinsons’ trust, but secretly plans to disarm them, paving the way for its master to arrive and capture the family for experimental purposes.
Seeking shelter from a storm, Penny and Dr. Smith discover a large mirror with a platinum frame, and Smith becomes fixated on its potential wealth. After Penny’s pet bloop, Debbie, enters the mirror and returns with a bell, Smith dismisses it—until he sees Penny accidentally fall into the mirror and enter a pocket dimension. Inside, she meets a boy who promises endless fun and eternal childhood. But Penny is desperate to escape, especially as a terrifying creature begins to hunt her. Meanwhile, unaware of the danger, Dr. Smith attempts to dismantle the mirror, risking trapping Penny inside forever.
Will and Dr. Smith encounter a boy named Quano, from a race of disciplined warriors. Quano reveals he’s been sent to the Robinsons’ hostile planet to prove his bravery, as he is destined to succeed his father as ruler. As part of his test, Quano must challenge someone to a contest of strength and skill, and he chooses Will. Dr. Smith overhears Quano’s father plotting to eliminate the Robinsons if Will wins, to hide his son’s failure. Smith then attempts to strike a deal with Quano, offering to help him ensure Will loses the contest in exchange for a ride back to Earth.
A freak storm destroys the Robinsons’ garden and condenser unit, forcing them to ration protein pills. Dr. Smith and Will discover alien advertising signs leading to a bazaar run by a space trader. The trader offers amazing goods and food from across the galaxy, but his prices are too high for the Robinsons, who need all their equipment. Desperate for a meal, Dr. Smith offers to trade the Robot. When the Professor finds out, he demands Smith retrieve the Robot, but the trader tricks Smith into signing himself over as a slave. The Robinsons soon discover the merchant has a weather-controlling machine, realizing they’ve been swindled, and work to rescue Dr. Smith.
Will finds a golden crown and is hailed as the new king of Andronica. Convinced the role is too much for him, Dr. Smith persuades Will to give up the crown. Smith enjoys the royal perks but soon learns the aliens plan to sacrifice him, as they regularly choose an outsider for this fate. Meanwhile, a kind clone of Smith causes the Robinsons to suspect something is wrong, realizing the real Smith is in danger.
Will, Penny, and Dr. Smith are attacked by a werewolf and begin tracking it. Their search leads them to a family of hillbilly farmers who seem to worship the strange plants they grow. Tensions rise when the Robinsons discover the aliens are stealing their equipment, and Judy becomes jealous as the farmer’s daughter, Effra, flirts with Don. Meanwhile, Smith woos the mother, Sybilla, with the sole intent of securing a ride back to Earth. His plans fall apart when he realizes Sybilla and Effra are witches, and her son, Keel, transforms into the werewolf under the full moon.
Penny meets an interstellar fugitive named Ohan and helps him, receiving a talking disc that leads to a hidden treasure. Soon after, a galactic lawman named Bolix arrives, searching for Ohan, though his true target is the disc. When Dr. Smith learns about it, he follows the disc to the treasure—a box containing a metal collar that gives him the power to turn anything he touches into pure platinum. However, the collar becomes a curse when it won’t come off, and Smith accidentally turns Penny into a platinum statue.
While searching for water, an earthquake traps Will and the Robot in an underground world, where Will awakens a sleeping princess with a kiss. She insists he join her, while the Professor and Major West are captured and brought to an ancient city. The princess’ Major Domo reveals Will is destined to fulfill a prophecy by becoming her consort as she leads an invasion to conquer the universe, starting with Earth.
Will and Dr. Smith discover an alien spaceship, which the Robot claims can travel anywhere in the universe. When Will enters the craft, the hatch closes, and he is taken on a wild journey into the sixth dimension. Exposed to cosmic forces, Will returns with superhuman intelligence. Eager to gain similar powers, Smith takes a ride in the ship, but instead returns as a frail old man and blames Will. Using his newfound intellect, Will works to restore Smith’s condition, but a scaly alien soon arrives, furious that his ship has been tampered with.
While exploring a cave, the Professor encounters a ghostly entity named Canto, who begins to possess his mind. Back at the ship, he becomes hostile and fatigued, leading Dr. Smith to suspect a breakdown. Canto grants the Professor the knowledge to repair the Jupiter 2, but as the family realizes he’s under alien control, they race to stop him before the entity fully takes over.