Aunt Agatha is cold and cruel. She refuses to loan Don and Christine Farmer any money.
The Farmers's twin daughters, Kelly and Lynn, 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 look like each other. Agatha found the moonstone but hid it from her sister and instead began using the magic it possessed 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.
Aunt Agatha discovers that the Farmers have twins and that they are a threat to her if their powers are combined. She attempts to get rid of them.