When siblings Pip and Tim move with their parents to an old English country estate and hear a strange knocking from within the walls of the ancient home, they can hardly believe their eyes: A mysterious boy, the son of a medieval alchemist, emerges and claims that he has been asleep for nearly six hundred years.

Sebastian reveals that his father’s evil enemy, de Loudéac, has also awakened from a centuries-long slumber and is determined to use the secrets of alchemy to evil ends. Soon, Pip and Tim find themselves entangled in a web of intrigue, sorcery and horror, as they join Sebastian in his quest to foil de Loudéac's villianous scheme. But can the madman be stopped?