A long time ago, a dark fog descended over Camp Spirit Moon. This fog turned all of the camp's residents into ghosts. Now, if any members of the camp try to leave, they will dissipate into the fog that turned them into ghosts. The ghosts need to possess a human body in order to escape.
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. Alex and Elvis sing camp songs together around the campfire; Alex's signing sounds good, but Elvis's singing sounds very bad.
Much later in the story, Elvis tells Alex that Uncle Marv's story was true, and all of the campers are ghosts. 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 hears Alex humming very poorly. Harry deduces that Elvis successfully possessed Alex.
Elvis seems to really enjoy singing, but he is incredibly bad at it. Though he initially acts very nice to Alex, Elvis is constantly looking out for his own personal interests. Much like Lucy, Elvis is so tired of being trapped at Camp Spirit Moon that he's willing to forcefully possess Alex in order to escape.
Elvis is a short, blond haired boy.