The film follows a boy named Milo. Milo is just beginning summer but his mother gives him chores and tasks like weeding the garden or eating his vegetables. But after Milo tints his sister's face purple, his mother sees no humor in this. She orders him up to his room. After an argument with his mother in which Milo says "I don't see what's so special about mothers!", Milo goes to his room. After falling asleep, Milo does not hear the rumble of the rocket landing outside. After, Martians enter Milo's house and take away his mother. Milo realizes that he has to rescue her. Milo embarks on an adventure to rescue his mother.The film is based on a children's picture book by Pulitzer Prize winning cartoonist Berkeley "Berke" Breathed, author of the comic strip Bloom County.