When Susan Murphy is unexpectedly clobbered by a meteor full of outer space gunk, she mysteriously grows to 49-feet-11-inches tall and is instantly labeled a “Monster” named Ginormica. The military jumps into action, and she is captured and held in a secret government compound filled with other “monsters” like herself. This ragtag group consists of the brilliant but insect-headed Dr. Cockroach, PHD; 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 time is cut short however, when a mysterious alien robot lands on Earth and the motley crew of Monsters is called into action to save the world from imminent destruction.