Kat (Ricci) and her eccentric dad, Dr. James Harvey (Pullman), a self-styled 'ghost therapist', shows up on the doorstep of the dilapidated Whipstaff Manor. Hired by Whipstaff's scheming owner, Carrigan (Moriarty), Dr. Harvey has to exorcise the manor of a friendly but lonely young ghost named Casper, and his three incorrigibly odious uncles, so that she can get her hands on the macabre manor's fabled treasure. As the ill-mannered ghosts go out of their way to scare the 'fleshies', Casper finds himself becoming best friends with Kat in this funny and lively story.