Harry and Alex Altman are sent to stay at Camp Spirit Moon. During one of the camp's campfire gatherings, Harry befriends a girl named Lucy, and Alex befriends a boy named Elvis. At the gathering, the camp's leader, Uncle Marv, tells a strange ghost story; a long time ago, a dark fog supposedly descended over Camp Spirit Moon, and this fog turned all of the camp's residents into ghosts.
Much later in the story, Elvis tells Alex that all of the campers are ghosts, and they can't escape the camp unless they possess a human body. Elvis tries to possess Alex against his will, but Alex manages to avoid this. Around the same time that this happens, Lucy tries to possess Harry. After this, Harry gets his brother, and the boys attempt to run away. The other members of the camp try to stop them.
The ghostly campers eventually surround the boys. All of the ghosts begin because they can't decide who will get to possess the boys. The fighting causes the ghosts to blend together into a smokey mist. The mist dissipates, allowing Harry and his brother to leave. However, Harry soon discovers that Elvis successfully possessed Alex.
Alex is eleven years old, tall, and thin. He has straight black hair, dark brown eyes, and a serious face.
Alex really loves to sing, and — to his brothers disapproval — Alex loves to show off his beautiful voice. Like Harry, Alex never believed in ghosts until their encounter with them at Camp Spirit Moon.