When William learns that his favorite caretaker Mrs. Phillips is leaving, he is devastated. But then she gives him her parting gift--a mysterious model castle that has been in her family for years. The castle is perfect in every way, with a drawbridge, a moat, and a fingerhigh knight to guard the gates. It's almost too real.

Sure enough, when William picks up the tiny silver knight, Sir Simon comes alive in his hand and tells William a mighty story of wild sorcery, wizards, and a kingdom in need of saving. Hoping the castle's magic holds the key to getting his friend to stay, William embarks on a fantastic quest to another land and another time--where a fiery dragon and an evil wizard are waiting to do battle.