The Witch's Sister (Paperback, 1st Aladdin Paperbacks ed)

When the darkness,
tolls the hour,
I shall have you
in my power...

Lynn and her best friend, Mouse, are positive their neighbor, Mrs. Tuggle, is a witch. And they suspect the old woman is forcing Lynn's sister, Judith, to join her coven to witches. But Lynn and Mouse can't prove anything and their parents don't believe them. the girls are desperate to expose Mrs. Tuggle's evil nature, especially since her actions are becoming more threatening everyday.

Now Lynn's parents have announced that they're going away for the weekend, leaving Judith and Mrs. Tuggle in charge. Can the girls outsmart Mrs. Tuggle and save Lynn's family -- or is the dark magic too strong to conquer?