R. L Stine

Wendy is excited when she spots a cat charm in Mrs. Bast's booth, but Mrs. Bast refuses to sell it to her. She warns Wendy that it isn't a cat charm-- it's a "werecat" charm and it's dangerous. Wendy doesn't care, she grabs the charm, throws down some money, and runs. That night, at the stroke of midnight-- Wendy starts to change.