When Will and Smith are hunting for precious minerals, they come across a strange alien spacecraft. Everyone comes to inspect it and the Robot says it is a “special delivery space vehicle” that can travel faster then the speed of light. He warns, however, that flying it could prove to be dangerous.
John and Don decide to give the spacecraft a inspection in the morning. Smith can’t wait and orders the Robot to go in for a closer look. An alien voice gives a loud warning, then shoots the Robot with an energy beam. Smith takes Will away and tells him to keep quiet about the incident. That night, Will sneaks out of the Jupiter 2 to repair the Robot. After doing so, he cannot resist the temptation to investigate the craft and gets inside. The door shuts behind him and the ship blasts off!
At the Jupiter 2, the Robinsons witness the lift-off and the craft's return shortly afterwards. They rush to see if Will is safe; the boy is physically sound, but he is acting strangely—he has apparently unlocked the secrets of the universe and his brain is now functioning on a much higher level then anyone else’s.
With his new-found genius, Will finds he can no longer relate to anyone and becomes frustrated and depressed. Dr. Smith is intrigued by Will’s increase in intelligence and decides to increase his own mind in the same way. He asks Will for tips on piloting the vehicle and goes to the alien ship to make a flight. When he lands, though, the Robinsons find his journey has had far different results; instead of making Smith a genius, it has made Smith into a decrepit old man.
Everyone feels very sorry for Doctor Smith, but they do not know how to reverse the process.. John, Don and Will conduct many tests with a flight simulator, but they make no progress. Will finally decides that the only solution is for Smith to fly the ship again, but with its energy field in reverse. Without his parents' permission, he takes off to try the experiment with himself first. Just as Will’s ship blasts off, another spacecraft lands nearby. An angry alien emerges yelling. The Robot translates his message as a protest against the theft of his ship. The alien takes Smith hostage until Will returns.
When Will returns, he has been restored to his normal self. He begs the alien to let Dr. Smith make a reverse flight so that he can get to be restored to his normal age. The alien himself takes Dr. Smith on a short flight, and when they return, Smith too is restored to his true age.
- The motif of an experimental craft mutating the pilot was revisited in the 1996 Star Trek: Voyager episode "Threshold". The scenerio of a child (or childlike person) being given extraordinary intelligence was redone in the 1996 film "Phenemenon".
- The stores of the Jupiter 2 are well stocked, as they apparently contain an old-fashioned wheelchair for the elderly Dr. Smith.
- The alien has an interesting psychology - it is advanced enough to create an incredibly complex spaceship but can only communicate with the Robinsons using grunts and non-verbal threats.
- The speed of the alien craft is stated as "speed of light squared." This is around 35 billion miles per second, or fast enough to go from Earth to the Galactic Center in about two months or from Earth to the Andromeda Galaxy in about ten years (relatively speaking).
- Why did Doctor Smith fall into that sand pit? He didn’t trip or anything, he just suddenly seems to tip forward for no reason and fall in. Once Will had saved him from the pit, why didn’t they leave some kind of a marker so nobody else would suffer the same fate?
- Why did the Robot stand there and let Will enter the alien spacecraft? The Robot was perfectly aware that it could be dangerous to do so. Isn’t he supposed to keep Will safe?
- Once the spacecraft took off with Will inside, why didn’t Robot immediately rush to tell the Robinsons? He really took his time about it, and when he did tell them, he just kind of casually wandered over and mentioned it.
- Where did they get the cane and wheelchair for old man Smith?
- Why does Smith put his old man clothes over top of his regular clothes?
- When the Robinsons speak to the alien visitor, he doesn’t understand them and the Robot needs to translate. But when Will shows up and speaks to the alien, the alien understands him perfectly without translation.
- Exactly how long was Doctor Smith gone when the alien took him away? It seemed like it couldn’t have even been a whole day, but the Robinsons had already written Smith off as dead and set up a memorial!