In the year 1997, the Robinson family is cryogenically suspended before their launch into space in the space-saucer Gemini 12 on man's first mission to colonize a planet orbiting Alpha Centauri.
Soon after leaving Earth, a meteor swarm sends the Gemini 12 spiraling out of control, ending in a crash landing on an unknown planet. The Robinsons survive the crash and set up camp, but their preparations to head south to avoid the sudden onset of the cold season are hampered by One-Eye, the giant cyclops, trapping John and Don in a cave.
After Will saves the men, and Penny is recovered after a turtle ride, the travellers journey to the tropics encountering along the way, the One-Eye again, fierce electrical storms, an underground city and a stormy sea crossing where they become caught in a whirlpool.
Spock commands a stranded away team when their shuttlecraft is marooned on a planet with hostile natives.
Dr. Tony Newman prematurely enters the government's Time Tunnel project, and the project head, Doug Phillips, must go back to save him as they both fight for survival on the sinking Titanic.
Luminous aliens capture Dr. Smith with the plan to replace their burnt out computer with his brain. Smith bargains with them, and they decide to use Will's brain instead.
Professor Robinson discovers that the planet's orbit will bring immense heat on the spaceship. With that knowledge, the Robinsons take off in the Chariot and head south. Dr. Smith stays behind because he believes them to be lying, but soon realizes the orbit is odd. There are periods of extreme cold followed by equally extreme heat. The Robot is sent to tell the Robinsons and they try to return to the Jupiter 2. They must brave various geographical areas and the strange weather before returning to the Jupiter 2 where they are most safe.moreless
Professor Robinson 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.moreless
Professor Robinson attempts to explore a planet that the family is planning to land on. Dr. Smith has sabotaged his para-jet propulsion system, causing it to fail. Smith has also sabotaged the propulsion system of the Jupiter 2. Major West crash lands the ship on the planet so that he and the family can rescue the Professor.moreless
The Jupiter 2 is pulled into a giant alien spaceship where there are advanced rock-like creatures. John and Don look for maps and equipment while Dr. Smith and Will look for trouble.