It's Halloween, and The Plaza's most notorious poltergeist is coming out to play. But when Eloise is accused of trying to scare the guests and the staff at the stately hotel, she realizes that the only hope of clearing her name lies in solving the mystery of a frightening phantom. Everyone in The Plaza knows the name Diamond Jim Johnson, but few believe that he has really returned from the dead to haunt them as the legends claim. While Eloise does her best to convince everyone that Diamond Jim's ghost is currently drifting through the hallways of The Plaza, no one believes her. Later, in order to reverse Diamond Jim's curse and save the hotel from some very real monsters, Eloise draws on her own supernatural powers of investigation.