While bowling, Smith, Will and the Robot are drawn to a mysterious cave where an equally mysterious trio of aliens greets them and offers gold in exchange for the Robot. Smith is ready to agree, but Will firmly refuses. The aliens declare that they will get what they want in any case, a statement which worries the Robot.
Back at the Jupiter 2, Will explains what happened to the rest of the family. Everyone is upset, but they try to reassure the Robot that they will protect him. That night, the aliens send a message to John (via his chess piece) that they wish to speak with him. John and Don go to the cave. Again, the aliens offer riches in exchange for the Robot. John refuses, and the aliens threaten to steal the Robot instead. The family is confident that their force field will prevent the aliens from entering the space ship, but the Robot is certain he is doomed and becomes very depressed. The three aliens later enter the Jupiter 2 in spite of the force field. They approach the Robot and insist he come with them, threatening to harm the family if he refuses. Fearing for the Robinsons’ safety, the Robot agrees to follow them back to their cave.
The next day when they notice the Robot is gone, John and Don go back to the cave and find the Robot in pieces. The aliens say they will return the Robot when they have finished studying him, but that Don and John may take the Robot’s head back with them. When the aliens return the rest of the Robot, still in pieces, Will, John and Don all work to reassemble him. Almost immediately, strange things begin to happen with the Robinsons’ equipment. John suspects that the three aliens are somehow responsible.
The Robot reveals that he overheard the aliens’ plan to build a machine to control other machines. John and Don set off to destroy the machine and Will and the Robot secretly follow along. After confronting the aliens, a fight ensues. The Robot is able to destroy their machine, and the aliens disappear.
- This is the shortest episode of the series, at 49:21. Not counting the unaired pilot (No Place To Hide at 52:10), West of Mars is the longest episode, at 51:51.
- In the scene where the Robot is being re-assembled, his power pack is installed twice.
- Will and the Saticon display great strength when they cavalierly toss around the Gold bowling ball at the beginning of the episode. A solid gold bowling ball would weigh over 200 lbs. Perhaps they should have participated in "The Deadly Games of Gamma Six".
- Using a phrase that will become familar to fans of "Star Trek", the aliens tell the Robot that "Resistance is futile".
- Will and Smith are bowling at the beginning of the episode. However, all the bowling equipment was left behind on the previous planet in the episode “Blast Off Into Space.”
- When the Saticons state that no human being can destroy their evil machine, Don and John just take their word for it. They don’t even try.
- When the Robot is finally put back together, several bits of electronics seem to be still left on the table.
- Doctor Smith gets on an exercise bike. Of his own free will!
- The Robot hides from the aliens in a previously unseen storage room. it appears to be among the staterooms.