The #1 bestselling chapter book series of all time celebrates 25 years with new covers and a new, easy-to-use numbering system! Jack and Annie must save stories that have been lost in history. Morgan, the magical librarian of Camelot, sends them to find the books in the ancient worlds of Roman Pompeii, imperial China, Dark Age Ireland, and classical Greece. Will Jack and Annie be able to save the stories in their darkest hours???or will the books be lost forever? Books in this set include: Vacation Under the Volcano (#13), Day of the Dragon King (#14), Viking Ships at Sunrise (#15), and Hour of the Olympics (#16). Did you know that there???s a Magic Tree House book for every kid? Magic Tree House: Adventures with Jack and Annie, perfect for readers who are just beginning chapter books Merlin Missions: More challenging adventures for the experienced reader Super Edition: A longer and more dangerous adventure Fact Trackers: Nonfiction companions to your favorite Magic Tree House adventures