All the Lovely Bad Ones — Mary Downing Hahn

TRAVIS AND HIS SISTER, Corey, can't resist a good trick. When they learn that their grandmother's quiet Vermont inn, where they're spending the summer, has a history of ghost sightings, they decide to do a little "haunting” of their own. But their supernatural pranks awaken something dangerous, something that should have stayed asleep. Only Travis and Corey can lay to rest the spiteful spirit they've stirred. This means discovering the secret of Fox Hill and the horrors visited on its inhabitants years before...