A day at the playground starts out with a chalk wall to draw on, a water wall to splash in, a climbing wall to clamber up, and a wall of kids playing an all-in-good-fun game. But it isn't long before one child is excluded, as another child leads the rest in building a castle wall that comes between them and the child they are leaving out. There are other unkindnesses, and of course, hurt feelings. But when the bully bellows "MINE," declaring the castle they have built together as his alone, he alienates all the other children. And being alone in the castle turns out to be surprisingly lonely, especially when it looks like the other kids are having fun without him.