The #1 bestselling chapter book series of all time celebrates 25 years with new covers and a new, easy-to-use numbering system! Hold your horses! Jack and Annie must find four secrets of greatness for Merlin the magician. To start, they travel back in time to meet Alexander the Great. He should know all about greatness, right? But young Alexander is bossy, vain, and not great at all! How can they learn from him? It’s going to take a wild black stallion, magic from Merlin, and a lot of bravery to succeed. Are Jack and Annie clever and bold enough to complete their mission? Formerly numbered as Magic Tree House #49, the title of this book is now Magic Tree House Merlin Mission #21: 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 Super Edition: A longer and more dangerous adventure Fact Trackers: Nonfiction companions to your favorite Magic Tree House adventures