When Percy and his friends attempt to leave the park maze, they discover that one of the squirrels has helpfully wound up the ball of string that was meant to prevent them from getting lost. The book contains a fold-away maze poster to help Percy find the way out.When Percy and his friends attempt to leave the park maze, they discover that one of the squirrels has helpfully wound up the ball of string that was meant to prevent them from getting lost. The book contains a fold-away maze poster to help Percy find the way out.