When Marissa May is walking home from school late after a detention she meets someone, or maybe something, in a fog covered London park that will change her life forever. Marissa discovers that she has a rare ability to communicate with ghosts and Arthur, a ghost from nearby Hampton Court Palace, needs her help.With her mum’s hotel business on the line, the last thing Marissa needs is Arthur haunting the guests, but it turns out that ghosts can sometimes actually be good for business. But soon Marissa's powers bring her face to face with a young witch who is anything but friendly, and things go from bad to worse as the new theme park at Hampton Court Palace takes on a sinister dimension. School kids throughout London are given free virtual reality masks by the new theme park, but it turns out the masks are more than just a video game. As Halloween approaches, the city of London descends into chaos, and it seems Marissa and her new friends are the only ones who can stop the mayhem.