Cassie Potter and the Fellow Pranksters

Harry's older sister, Casablanca Lily Potter - but if you call her that, she'll hex your face off - goes to Hogwarts. While she's there, she meets Fred and George Weasley and Lee Jordan, three who share her love of pranking. She gains the nickname Firecracker and they become best friends. However, there's a Potions Master stalking her. Why? She has no idea.