The Halloween War — Francine Pascal

Jessica Wakefield is in big trouble! She told all  her friends at school that the Wakefield's house  was haunted. Now everyone wants to see Jessica's  ghost. Jessica's twin sister, Elizabeth, comes up  with the perfect plan they'll have a party with a  special appearance by a make-believe ghost. But the  Halloween party is even scarier than the twins  expected. Have Jessica and Elizabeth been outsmarted?  Or is the Wakefield house really haunted?