Storybound by Marissa Burt

When Una Fairchild stumbles upon a mysterious book buried deep in the basement of her school library, she thinks nothing of opening the cover and diving in. But instead of paging through a regular novel, Una suddenly finds herself Written In to the land of Story—a world filled with Heroes and Villains and fairy-tale characters.

But not everything in Story is as magical as it seems. Una must figure out why she has been Written In—and fast—before anyone else discovers her secret. Together with her new friend Peter and a talking cat named Sam, Una digs deep into Story's shadowy past. She quickly realizes that she is tied to the world in ways she never could have imagined—and it might be up to her to save it.