Ibb, curious about the lone castle in her town, forms a long-distant friendship with the guard and, despite warnings there is something fearful inside, accepts his invitation to enter.
In their magic treehouse, Jack and Annie are again transported to King Arthur's realm, where invisible beings, giant ravens, and mistaken magic spells have a duke's castle in an uproar on Halloween night.
Eight-year-old Jack and his younger sister Annie use the magic treehouse to travel back to the Middle Ages, where they explore a castle and are helped by a mysterious knight.