While the others are preparing the Jupiter 2 for a long-awaited lift-off, Will, Dr. Smith and the Robot are collecting ore samples. Dr. Smith is injured by an explosion, and, suffering from amnesia, refuses to return to the Jupiter 2. A strange beeping noise leads Dr. Smith into a cave, and Will and the Robot follow him. They find an ancient computer and other artefacts from a forgotten civilization, but aware that the Jupiter 2 will shortly lift off, the Robot strikes Dr. Smith, restoring his memory, and the three set off for the ship.
When they arrive, they find the Jupiter 2 has become an aging hulk with no sign of the Robinsons aboard. They begin to panic, but the Robot reassures them that the ship is merely an illusion created by the same force that lured Smith into the cave and leads them to the real Jupiter 2.
Dr. Smith and the Robot later return to the cave where the various alien devices tell him that he can become their ruler and restore the Dranconian civilization to its former glory. When the Robot, transformed into gold and acting rather uncharacteristically feckless, returns to the Jupiter 2, Will rushes to cave to find Dr. Smith. Smith, however, has taken on more and more of the appearance and attitude of the Dranconians and refuses to depart with the crew the next morning.
Will is distraught, but his father explains that if they miss their launch window there is no way of knowing when they might be able to leave the planet again. They nonetheless go to meet Smith but fail utterly in convincing him to return. Against his father’s order, Will makes one last visit to the cave and begins to cry at Smith’s refusal to accompany him back to the Jupiter 2. After he says good-bye to Dr. Smith and the Robot one last time and leaves, Smith finds that what remains of his humanity has been touched by the boy’s tears, and with the Robot’s assistance tries to reach the Jupiter 2 in time for take-off.
They are too late, and hear the ship’s engines while still some distance away. Despondent at being left behind, Dr. Smith is stunned to find that the Robinsons returned for him after picking up his approach on radar… he is so happy that he ignores Don’s sarcastic comment that they only came back for the Robot—a valuable piece of equipment.
- The props in the cave include a model of the Jupiter 2 that appears to be four feet in diameter.
- Though the Robinsons were going to lift off in this episode, the condition of the Jupiter 2's electrical systems is in question. In the second episode produced (and the fourth one aired) after this one, Trip Through the Robot, Don and John have just finished rebuilding the electrical system (probably blown out in Forbidden World) and can, once reactivating it, bring the ship up to full power in preparation for an eventual lift-off. This would seem to imply that the electrical system was not in working order at the time of The Cave of the Wizards.
- This was one of Jonathan Harris' two favorite episodes, the other being West of Mars.
- John makes a reference to the keys of the Chariot.
- At the start when Dr. Smith has amnesia, he refers to the ship as the Jupiter 2. However, the Robot had only previously called it the Jupiter.
- When the Robot hit Smith’s head with a rock, why did it make a hollow ‘clang’ sound? Why didn’t Smith get a cut or a bruise? It was an awfully big rock!
- When John and Don go to the cave to try to convince Doctor Smith to come with them, Don looks completely bored.
- Why is it called “The Cave of the Wizards” when there wasn’t a single wizard?
- When begging Smith to come back, Will claims that Smith often told him fond ‘stories of his family back on Earth.’ However, in the episode “The Curse of Cousin Smith,” we found out that Smith’s cousin Jeremiah was his only living relative, whom he hated.
- Why did the Robot have a pen?
- Why did the Jupiter 2 have such a strict "launch window?" When they missed it, why did they have to wait so long to take off again?