Gecko is a ghoul town northeast of Vault City. Its economy is based on the operation of an old, half-functional Poseidon Energy nuclear power plant. Harold is the de facto mayor of Gecko, while he is assisted by Lenny, who also serves as Gecko's doctor. The power plant is administered by Festus. Gecko's citizens are divided between the renewal cultists and the more ordinary ghouls, who resent the cult. The renewal cultists seek to "renew," i.e. become human again. They are headed by a giant, sentient mole rat who lives in an underground cave adjacent to the reactor, known as the Brain, who seeks to take over the world.