Dr. Smith causes a serious accident through carelessness in handling a fuel cell, despite warnings to take care. After John finds that everyone is uninjured, he is unable to get a clear account of what happened from Don, Dr. Smith, or even Will. Don then brings up other cases of Smith's recent negligence and expresses a hearty wish they were rid of him. Smith reacts in a huff and announces that he will leave the camp. When the time comes, though, he is somewhat taken aback when no one says a word to stop him.
Will soon begins to worry about Dr. Smith on his own, but his father assures him there is nothing to fear. Meanwhile, Smith has set up a small camp, and as night draws on, becomes increasingly afraid at being alone. Will later appears to check on him, suggests a better location for his camp, and the two go off. They soon come across the apparently ancient and decayed ruins of an alien spacecraft, and discover a strange helmet within it. Almost accidentally, they discover that the helmet has the power to materialize their wishes.
Smith asks him what he'd like. He'd like a bike or a telescope, but then he decides he wants an apple. Apples come raining down upon Smith and Will.
It soon becomes apparent that Will had snuck out of camp without permission, and he is forced to tell everyone where Dr. Smith is when his father discovers a basket of apples in his son's cabin, products of the wishing helmet. Don and John pay a visit to Dr. Smith, who grandly promises to use the device to create a new Jupiter 2. They next day he attempts it, but when only a small model appears, they deduce that the machine has certain limitations.
Although Smith remains ensconced in his now fabulously appointed camp, he graciously shares the helmet with the Robinsons. Very soon, though, it becomes apparent that having the means of making your fondest wishes come true has very serious negative effects on the various members of the crew. Even after John's stern words bring his family back to their senses, Smith continues to indulge his every whim. When he wishes for a servant, however, he has gone to far. A strange mummy-like being appears out of a locker in the aft of the ruined spaceship and moves toward him. Smith fears for his life and runs back to the Jupiter 2, the creature in pursuit. He arrives just as the Robinsons have discovered that everything they wished into existence has now fallen to pieces. When the creature arrives, John demands an explanation, but it is clear that the visitor is only seeking the helmet which Smith has hidden away. Eventually, John is able to bring about its return to the ruined ship and the creature retires with it back into the locker from which it emerged. When Will tries to follow, he finds only an empty, cobweb filled space, with no sign of the creature or the helmet. Will wonders why the alien took the device back and John tells him it was greed and selfishness—Smith asked for too much.
- The first instance in the series of an epsiode that is essentially a morality tale, the story also is the first in which anything necessary to the plot can literally be conjured up without concern about the actual science involved. Prof. Robinson fulfills his first role as the ethical conscience of the series and Dr. Smith as the avaricous fool.
- The mummy creature will return in "The Keeper: Part II", and the memorable sound he makes is used for the cloning machine in "His Majesty Smith". Also, the odd hook-nosed creature making a brief appearance after Smith shoots a bush is changed and reused in "The Keeper: Part II".
- The mummy creature's sound is a man making a whimpering noise, slowed down about 80%.
- This is the first of many times Smith is exiled from the Robinson camp.
- The miniature Jupiter 2 procured by the wishing machine is the 18" model used for space scenes throughout the show. It is also interesting that Dr. Smith chooses to manifest another Jupiter 2 as the result suggests the reason why the developers of the wish machine couldn't use it to repair their own ship.
- In the opening scene where Don and Will are working on the chariot the IBM logo can be seen on the top one of the electronic assemblies in the rack.
- The explosive nature of the gas used as fuel for the Chariot suggests it's made with hydrazine, a chemical often used as a propellant in manuevering thrusters in spacecraft.
- As in "A Change of Space", this is another LiS example of a creature that has a remarkably advanced civilization and yet can only grunt, howl, or gesture at our space family. And as the mummy creature only grunts, howls, and gestures, its exact motivations with respect to the return of the machine are just moral guesswork on the part of Prof. Robinson.
- The thought machine prop will return in "The Space Trader" as the Trader's language translation device.
- The wreck is convincing enough, but begs the question how the creature has survived this long and to where it disappears at the end.
- In this episode, we learn that apples are rare and precious commodities that the Robinsons do not have. However, in the episode “A Trip Through the Robot” we see Dr. Smith chomping on an apple like it is nothing special at all.
- When Don picks up the exploding fuel cell, why does he throw it -towards- the Jupiter 2 rather then away from it?
- John gets angry at Dr. Smith because he neglected his chores and caused the hydroponic garden to die. Knowing how lazy and inept Smith is, why would the Robinsons put him in charge of something as important as their food supply?
- Why does Penny fold her hands in prayer when using the Wish Machine? Is that necessary, or is she just being cute?
- Bang! The Chariot’s fuel pack explodes, but not before Major West manages to fling it to safety. But instead of bursting into fifty pieces of deadly shrapnel, it just disappears in a cloud of smoke!
- When Don is under the Chariot, Judy shows up in her new dress and hair-do courtesy of the thought machine. Wow, says Don as he re-appears from under the Chariot, then apparently bumps his head in his excitement. Only thing is the bump noise is made by his boot, and he doesn’t appear to bang his head at all.
- Maureen turns the force field on before the men have departed the spaceship’s perimeter. Oops, - ZAP!!…
- The buttons for the Jupiter II's glide tube must be universal. When Will is seen entering the elevator, he presses the rear buttons, which cause the safety gate to close and the contraption to descend. When Dr Smith enters the glide tube later, he presses the buttons above the gate and the same action occurs.
- When Dr Smith finally asks for too much from the thought machine, all the items at the Jupiter II become defective but oddly, not the items at Smith's campsite in the derelict alien ship. Later, all items at Smith's campsite disappear along with the alien. (We never hear if the same happened to items at the Jupiter II, which would have left Judy suddenly naked if, for some reason, she hadn't yet changed out of her ragged dress). Mmmm…
- Judy and Don sit down on two very comfy looking lounge chairs outside the Jupiter II when John calls a meeting. How these items of furniture made it on board before lift-off is anyone’s guess.
- Dr Smith: "We have the gift horse. Let's not examine its mouth too closely."
- Dr Smith: "I have the thought machine, and I can have anything I want. All I have to do is think and POOF!, (heh heh), it's mine!"
- Don: "When things go bad for no logical reason, I've always got an answer - Smith!"