When a meteor full of space gunk transforms Susan Murphy (Reese Witherspoon) into a giant, the government renames her Ginormica and confines her to a secret compound with other monsters, like bug-headed Dr. Cockroach (Hugh Laurie). When an extraterrestrial robot lands on Earth and begins a rampage, Gen. W.R. Monger persuades the president to send Ginormica and her fellow monsters to battle the machine and save the planet.