While spending the summer at their grandmother's Vermont inn, two prankster siblings awaken young ghosts from the inn's distant past who refuse to "rest in peace."

On his way to visit his aunt Sweetfur who is on vacation in the Pleasant Paw Hills, Geronimo Stilton--editor of "The Rodent's Gazette"--gets lost in a dark forest and seeks shelter in a run-down mansion unfortunately haunted by cats.

Ginny is unhappy when her family moves from Chicago to upstate Michigan for the summer; her father has a job restoring a 1930s mansion, but there are rumors about Woodmoor and the forest next to it: rumors about strange mutant creatures; Ginny, an aspiring mystery writer, is soon half convinced that the rumors are true, because something or someone is haunting the house--and she plans to investigate, with the help of Will, the older boy who lives...