When the often-fearful eleven-year-old Tom discovers a slimy green ghost in his cellar called Hugo, he is understandably afraid. However, Tom soon realises that Hugo, who is an ASG (Averagely Spooky Ghost), 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! To help get rid of this AIG, Tom and Hugo enlist the services of a professional Ghosthunter, Hetty Cuminseed. Will the unconventional trio overcome their differences, and manage to defeat the evil Ancient Ice Ghost, and save the town from an icy end?