When California girl Susan Murphy is unwittingly clobbered by a meteor full of outer space gunk on her wedding day, she mysteriously grows to 49-feet-11-inches tall. The military jumps into action and Susan is captured and secreted away to a covert government compound. There, she is renamed Ginormica and placed in confinement with a ragtag group of Monsters: the brilliant but insect-headed Dr. Cockroach, Ph.D.; the macho half-ape, half-fish The Missing Link; the gelatinous and indestructible B.O.B.; and the 350-foot grub called Insectosaurus. Their confinement is cut short, however, when a mysterious alien robot lands on Earth and begins storming the country. In a moment of desperation, the President is persuaded to enlist the motley crew of Monsters to combat the Alien Robot and save the world from imminent destruction.