It is the Middle Ages. Eleven year old Roland has been left as the master of his family's castle. He believes his mother is dead. His father has gone away on a mysterious quest. His wicked Uncle Dagarth, Auntie Hildegrind and his two bullying cousins have taken over the castle on the pretext of looking after him. What they really seek is the castle's treasure, which they believe to be mere gold or silver. Neither they, nor Roland, know the castle's real secret. At it's heart is an invisible, magic tower, which is a trove of secrets and a route to other worlds.
Roland is not alone. His father has left Firebrace, a trusted servant, as his son's mentor. Roland also has a friend called Oliver, a boy from the nearby village.
A visit to the castle by two strangers sets in motion a series of events which lead to Roland discovering the secrets of his castle and which sees he and his friends going on a quest to other worlds.