Jack and Annie aren't great baseball players...yet! Then Morgan the librarian gives them magical baseball caps that will make them experts. They just need to wear the caps to a special ballgame in Brooklyn, New York. The magic tree house whisks them back to 1947! When they arrive, Jack and Annie find out that they will be batboys in the game, not ballplayers. What exactly does Morgan want them to learn? And what's so special about this game? They only have nine innings to find out!