The movie opens with poachers attacking a group of gorillas. Animal preservationists fight the poachers, which ends with one gorilla and a young girl's mother dead. In the melee, a particularly large gorilla baby attacks the head hunter and bites his thumb and forefinger off. The films immediately passes into the future and the young girl has grown up to be Charlize Theron and the gorilla has grown to be 15' tall and weighs 2000 pounds. The two are best friends who play together. When poachers again appear, a representative (Bill Paxton) of a California wildlife refuge convinces her to transfer the gorilla she has named Joe Young to the refuge. Of course, once there the former hunter shows up seeking revenge. Terrorizing the gorilla without letting his human handlers know, the gorilla goes on a rampage across Los Angeles.