The episode begins with the Jupiter 2 taking up orbit around an alien planet. The atmosphere of the planet may be dangerous to humans so they hesitate to land. When a strange mist suddenly engulfs the spaceship, the Robot identifies it as a hostile life form.
As Will and Dr. Smith sit in their cabins, the alien mist surrounds them and a voice speaks to them. Smith and Will both tell the voice they want to be left alone and the voice promises that the wish will be granted. Smith is then transported to a dark, spooky, misty dimension. The voice speaks to him again, demanding that he admit he hates the Robinsons. Smith says he does not and is transported back to his cabin.
Shortly after this Maureen vanishes from the galley while preparing breakfast. Penny and Judy, who were standing nearby, are baffled by this and inform John and Don. No one is able to locate Maureen, and moments later Judy disappears as well. Will, Smith and Penny search the entire ship for them, but cannot find either them anywhere.
The spooky mist surrounds the Jupiter 2 again and bangs violently on the hull for a while before disappearing again. The Robot says the creature feeds on hatred and fear, which makes everyone worried. Penny is the next to vanish and she finds herself in the misty dimension where Judy and Maureen already are. The alien voice torments the women and does its best to scare them.
Don decides to fly the space pod down to the alien planet in case the women have somehow been taken there but is unable to do so. Shortly afterwards he too is transported to the misty dimension. The Jupiter 2 begins to lose altitude and is slowly drawn toward the planet. John ties himself and Will together so they will not lose one another, but it does no good. Dr. Smith vanishes, and then John, and the Robot as well.
Will is very frightened because he is now on the ship all alone. He searches once more in the hopes of finding someone. He finds Dr. Smith, who has been possessed by the spirit of the evil alien mist. The possessed Smith is very cruel to Will and tries to scare him by telling him his family is gone forever. He demands that Will land the Jupiter 2 on the alien planet below.
Will runs away and the possessed Smith chases him. They run to the ship’s power core where Will finds out to his horror that the space creature is his future self. If the ship lands on the planet, Will will be stranded on the ship, unable to venture out due to the poisonus atmosphere. As the evil mists slowly seeped into the Jupiter 2 over time, Will would slowly be transformed into the space creature. In an attempt to end his suffering, he would then try to kill his past self.
The young Will Robinson attacks his future self; the creature weakens, falls into the power core, and is destroyed, and Will's fate is changed.
- At one point "Dr. Smith" yells out "I AM YOUR ID", to which Will replies, "Don't try to scare me with your big words."
- In perhaps the cheapest costume to appear in LIS, the monster's final apparition is an actor with a bedsheet thrown over him.
- Ron Gans provided the distinctive voice for the evil alien Armus in the Star Trek:The Next Generation episode "Skin of Evil." It is mere coincidence that Armus looks like a bedsheet, albeit one covered in black tar.
- The Jupiter 2 seems to grow an extra deck in order to accomodate the Power Core. Also interesting is that despite the fact the Power Core functions from a material "made by concentrating certain radioactive ores" Dr. Smith and Will can stand right next to it with no ill effects. Because the reactor is in the bottom of a reactor shaft.
- Was it Smith who summoned the Evil Entity, or was it Will? That point is very unclear.
- The door to the Jupiter 2's power core had a sign on it that said “Danger, Radiation!” Doesn’t that mean Will should have put on some form of protective gear when venturing inside?
- Why do Will and Penny walk the five steps it took to “search the galley?” They could easily see the entire area from where they were previously standing.
- The future Will Robinson was instantly destroyed as he plunged down the reactor shaft.