The two siblings, Jack and Annie, return to visit the magic tree house. As they read a book about knights and the middle ages, Annie is intrigued by the Black Knight and the mysterious quest one must successfully complete before becoming a knight. When she wishes to visit the castle in the book, the siblings are whisked away to medieval times. They set off to learn more about the Black Knight and his quest, experiencing a grand medieval feast, escaping through secret tunnels and dancing with enchanted suits of armor, all in an effort to find their way back home.