Jack and Annie are off on another thrilling adventure, this time on a special mission from Merlin the magician! Their quest? To uncover four secrets of greatness. To begin, the magic tree house whisks them away to ancient times, where they hope to learn from the legendary Alexander the Great. But when they arrive, young Alexander isn't the wise, powerful leader they imagined. Instead, he's a bossy and vain prince! How can Jack and Annie possibly learn about true greatness from him? It will take a wild black stallion, a dash of Merlin's magic, and all of Jack and Annie's bravery and cleverness to succeed. Join them as they navigate this challenging historical journey and discover what it truly means to be great in this exciting Merlin Mission!