Through a series of not-so-happenstance meetings, Mads and Billy realize that desperate mothers and rescue missions are not the only thing that bonds them. Billy carries a map in his pocket; the one of the museum from The Mixed-Up Files of Mrs. Basil E. Frankweiler; and it's his dream to visit the museum one day. And though book-loving Mads is expected to return home to her already-decided future, her dream is to run away to a life of her choosing. As the unlikely pair fall hard for each other and as the summer draws to a close, Billy and Mads must decide whose story to follow: their family's or their own.