Martin and Andy (Andromeda) play tennis, Martian-style. Detective Bill Brennan and his son Brad try to spy on them. Non-human Andy is worried about a medical check-up at school. A robot duplicate creates issues at the school.
Andy has to do a school report on a planet. No one believes the truth about his home planet of Mars. After a disagreement over the matter he gets expelled. Insanity ensues.
Andy is feeling homesick. After missing curfew, Andy and Katie are grounded for a week. They sneak out in the spaceship for a quick trip to Mars. The Brennan's snoop.
Andy and Katy have a high school dance coming up. A tomboyish girl classmate of theirs is great at all kinds of sports, and she can also beat her male classmates (including Andy and Brad Brennan) in sports. But no boy has asked her to the dance. Katy tries to get Andy to ask her. In one scene, Andy uses his powers on a stack of footballs.
Katy uses Martin's new time machine to do her Ancient History homework on Cleopatra. Cleopatra is accidentally brought to the present and tries to woo Uncle Martin.
Uncle Martin invents a robot that does everything you tell it to do. But when Uncle Martin goes to another country, Officer Brennan's son Brad steals the robot and tries to make money from it.
Okie is having trouble making Earth animal-friends until Uncle Martin gives him a Okie-Talkie translator so he can talk to other animals.
Andromeda comes down with a Martian disease called "tripleosis," in which he first turns colors (including "Yerple"), and then splits into three personalities: positive, negative and indecisive. Uncle Martin has to find them in time, or Andromeda will disintegrate.
Lorelei wants to redecorate the garage. Martin shrinks his spaceship to hide it. Thinking it's a toy, it winds up in the hands of Brad.
Andy uses Martin's new untested Personality Reversal Ray device without permission. It affects Chump, Brad, and Brennan. There's a scavenger hunt.
Two meteoroids crash above Earth spilling an allergen that Martians are allergic to. Martin and Andy have side-effects.
Martin's new NYSINYD machine makes things vanish. Andy's teacher meets with Martin about Andy failing History. Due to a mishap, the teacher disappears.
Andy decides to drop out of school, but changes his mind after getting the hots for Phyllis, a new girl. Meantime, Brennan the snooping secret policeman gets soaked three times in one movie as his spying schemes go awry.
Martin experiments with a device to make plants happy. Chump gets into trouble and becomes depressed. Andy tries the happy device on Chump only for it to go awry.
Lorelei tries matchmaking by introducing her niece to Andy, the teenage Martian boy. The lovebirds attend a performance by Gertrude Schneeman, who recites her own unpublished poetry and accompanies herself on a snare drum. Meanwhile, secret policeman Brennan tries unsuccessfully to spy on Uncle Martin.
The highway constructors want to destroy the family garage to put in an off-ramp. Martin tries to save the garage, and hence, his spacecraft.