Twelve-year-old Kim is spending a summer on Shag Island in Maine. The island has been in her family for generations, but now Kim and her mom have to help her great-grandfather prepare to sell both the island and the mansion that sits on it. Everything goes smoothly until Mom is called away on business and Kim and her great-grandfather find themselves alone on the island with some strange happenings. The more Kim investigates the spooky music and bright flashing lights, the more she realizes that they are in grave danger. Now Kim must discover what—or who—is haunting Shag Island.