A pair of human twin girls who have the names of Rebecca and Eva, are carried off by a big black spider to the House Of Horrors, where the monsters of the Goosebumps series live. Slappy takes in the girls and raises them with help of the werewolf, Will Blake, Murder The Clown, Graveyard Ghouls, the Annihilator 2000 robots, and Fifi The Vampire Poodle.