When their magician grandpa is imprisoned in a snow globe, Hedy and Spencer—with cousins Jelly and Max—go in search of a magical way to free him in the final instalment of the House on Hoarder Hill trilogy. The Spellbound Tree is the source of all magic, but to find it the talented children must fight their way through the catacombs of Paris, with the help and hindrance of ghosts and monsters.