One summer day in Frog Creek, Pennsylvania, a mysterious tree house appeared in the woods. A brother and sister named Jack and Annie soon learned that the tree house was magic—it could take them to any time and any place in history. They also learned that the tree house belonged to Morgan le Fay, a magical librarian from the legendary realm of Camelot.

After Jack and Annie traveled on many adventures for Morgan, Merlin the magician began sending them on “Merlin Missions” in the tree house. With help from two young sorcerers named Teddy and Kathleen, Jack and Annie visited four mythical places and found valuable objects to help save Camelot.

For their next four Merlin Missions, Jack and Annie were told they must travel to real times and real places in history and prove to Merlin that they could use magic wisely.

Now Jack and Annie must save Merlin himself. Morgan le Fay has asked them to find four secrets of happiness to help Merlin out of a deep sadness. Having found the first three secrets, they are waiting to find out where they are going to search for the fourth…