As a thank-you from Merlin and Morgan, Jack and Annie are sent on what should be a vacation at a luxurious resort in Cozumel, Mexico, but is, by mistake, an adventure with ancient Mayans, instead.
When Jack and Annie travel back to the Kansas prairie in search of "something to learn," they gain an understanding of how hard life was for pioneers and they experience the terror of a tornado.
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.