His mother (voice of Joan Cusack) abducted by Martians intent on harvesting her maternal instincts to nurture their young, nine-year-old Milo (voice of Seth Green) stows away in an alien spacecraft bound for Mars in a bid to bring her safely back to Earth. Later, on the Red Planet, Milo befriends a subterranean-dwelling earthling named Gribble (Dan Fogler) and a spirited Martian lass named Ki (Elisabeth Harnois), who agree to help him locate his missing mother and confront the head alien in charge (voice of Mindy Sterling).
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