In order to avoid helping locate ore that the Robinsons need to repair their food purification unit, Smith pretends he is ill, then lies down and takes a nap. He is awakened by a large, hairy beast. He cries out, and Penny, Will and the Robot come running to see what the matter is.
They are all greeted by a man in a top hat who introduced himself as Marvello and tells them the beast was the Cosmic Monster, a part of his intergalactic circus. Smith immediately starts flattering Marvello in the hope of joining up with his circus and being taken back to Earth. Marvello is sad to learn the Robinsons are the only people on the planet, but offers to put on a show for them in exchange for supper. Smith takes the Robot away with him to prepare for his audition, a terrible song and dance act. In the process we learn that the Robot is also a terrible singer who cannot carry a tune.
The Robinsons go to the circus show and have a lot of fun. One act calls for audience participation, and Will volunteers. Afterwards, Marvello suspects Will might have psychic powers and determines to make him part of their entourage, whether the boy likes it or not!
Although Will enjoys materializing things with Fenestra, he is unwilling to leave his family. Smith is eager to go, but Marvello is unimpressed with his audition and says no. He does, however, offer to take Smith along as Will's manager if he can convince Will to join up. Smith agrees and comes up with a way to trick Will into doing as Marvello wants.
Smith sabatoges the food purification machine and then tells Will there will not be enough food to go around. He convinces the boy that the Robinsons would stand a better chance of survival without them. Will falls for the ruse and agrees to join the circus, sneaking off in secret with Smith.
The Robinsons find out and race to stop Marvello from taking Will. Marvello sics the Cosmic Monster on John, but Will uses his psychic powers in a futile attempt to aid his father. When Marvello sees how distraught Will is at the prospect of leaving his family, he realizes Will would never truly put his heart into a circus career and releases him.
- James Westerfield was not only an accomplished stage actor but also a set designer, producer, and director. He won two New York Drama Critics Awards for acting.
- Although he was a ‘reluctant stowaway,’ Smith has somehow brought along a straw boater and cane, not to mention a whole suitcase of belongings.
- Although the Robot is aware of Smith’s plans and disapproves, he doesn’t bother to inform the rest of the family until it’s almost too late.
- When Will visits Marvello to attempt the materialization trick for the second time, I can’t help but notice that he has a rather painful looking sore on his lower lip. Poor little guy!
- Smith continues to throw insults at the Robot. Some in this episode are: Chattering Magpie, Bumbling Booby, Cackling Cacophony, Cackling Clod, Traitorous Tin Plate, Tarnished Trumpet, Sanctimonious Scatterbrain.
- During the opening credits where Dr Smith Will, Penny and the Robot are approaching the camera, you can see the mechanical man’s tow cable in front of its tracks.
- When Marvello commands the furry cosmic monster back to its cage after fighting Vicho, it turns its head sharply, where you can see the bottom section of the detachable head mask quite clearly.
- When Dr Smith and the Robot are spying on the men who are trying to fix the food processor, the Robot leans forward on Smith, pushing him into a rock that noticeably wobbles!
- Marvello has never been to earth, and yet he uses religious terms common on earth: He speaks of certain events being "providential" and of someone going to their "eternal reward." Likewise he refers to Fenestra as a "mistress of the occult." How does Marvello know about these earth concepts?
- If Marvello travels the universe regularly, why does he not have instruments that can tell him how many inhabitants there are on a planet, and why would he not consult such instruments before going to the expense of bringing his show to a particular planet?
- Marvello's sudden change of heart at the end of the episode about forcing Will to go along with him is not very believable. He already knew Will's heart was not in going.
- In the Season 1 episode The Keeper: Part 2, Dr. Smith similarly manipulates Will and Penny into volunteering to leave the planet with the alien Keeper by deceptively telling them it's the only way to save the rest of their family and friends.