When the often-fearful eleven-year-old Tom (Milo Parker) discovers a slimy green ghost in his cellar he is understandably afraid. However, Tom soon realizes that the ghost named Hugo, is an ASG (Averagely Spooky Ghost). He is not only completely harmless but also desperately in need of his help. He has been banished from his haunted house by a dangerous AIG (Ancient Ice Ghost) who has moved in and is spreading an arctic cold over the entire town in the middle of summer! Tom and Hugo enlist the services of a professional Ghosthunter, Hetty Cuminseed. Hetty doesn't like children or ghosts very much but Tom and Hugo convince her to teach them the basics of ghosthunting. The three become an unlikely team - only with friendship, courage and self-confidence can they overcome their adversary, but will they be able to save the town?