ThePotterfamilyhasjustmovedtoarentedapartmentinSanFrancisco.HarryPotterSr.andhiswifeAnnearebringingthepackagestotheapartmentandtheirsonHarryJr.andtheirlittledaughterWendyAnnestaysonthesidewalk.Wendygoestothelaundryroom,shemeetsthewickedtrollTorokthatuseshismagicringtopossessWendyandtouseherformtotransformthedwellersandtheirapartmentintoothertrollsandhiskingdom.HarryJr.feelsthatsomethingiswrongwithhissisterandseeksouthelpwiththegoodwitchEuniceSt.Clairthatlivesinthebuilding.

一家人在度假小镇发现整个镇上居住的是妖怪的伪装成人类，正计划吃他们。