The Potter family has just moved to a rented apartment in San Francisco. Harry Potter Sr. and his wife Anne are bringing the packages to the apartment and their son Harry Jr. and their little daughter Wendy Anne stay on the sidewalk. Wendy goes to the laundry room, she meets the wicked troll Torok that uses his magic ring to possess Wendy and to use her form to transform the dwellers and their apartment into other trolls and his kingdom. Harry Jr. feels that something is wrong with his sister and seeks out help with the good witch Eunice St. Clair that lives in the building.