Kelly (Mary-Kate Olsen) and Lynn Farmer's (Ashley Olsen) parents, Don (Eric McCormack) and Christine (Kelli Fox), are deeply in debt and in danger of losing their home. During the Halloween season, they visit Christine's cold and cruel Aunt Agatha (Cloris Leachman) to ask for a loan, which is immediately refused. While the girls wait outside, they meet Agatha's grave digger (Wayne Robson) who tells them the story of Agatha's twin sister Sophia (also played by Cloris Leachman) who is trapped inside the house. He explains to the girls that Agatha's home once belonged to a powerful witch who, before being burned at the stake 200 years before, had hidden her moonstone, the rare gem which gave her power. As children, Agatha and Sophia, tired of being twins, heard the tale and began looking for the stone in hopes of using its power to no longer be identical anymore. Agatha found the moonstone but hid it from her sister and instead began using the magic it possesses to make her sister's life miserable. Years later on Halloween, Sophia and her fiancé George, now Agatha's butler, prepared to elope and begin their life together, but Agatha, out of jealously and rage, cast a spell that banished her sister into the netherworld through a mirror, which she keeps hidden in the attic. On the 7th year at midnight, this Halloween, the spell will become permanent and there will be no way for Sophia to be rescued.