Two sisters are told to go and play outside on a beautiful day. The little sister wants them to play together - but the big sister, instead, wants to sit under a tree with a book. So the younger sister decides to tempt her with a description of her super-cool, super-secret tree fort. Just what will it take to get her sister to look up? The promise of a water-balloon launcher in case of attack? A trapdoor to look at the stars? A crow's nest where they can see how many whales pass by or watch for pirates? Or the very best part of all, which can't be revealed, because it's a secret?