In a future where everyone lives in walled super-cities, Grace Lotts is curious and always has been. She wants to know why the Walls exist and what is beyond them. Not just what they teach in school, but what actually lurks in the Beyond. As she begins to dig for information, though, she discovers a plot more sinister than she ever could imagine. A plot to bring the Walls down, a plot to bring the Beyond inside. To the authorities, this is an impossibility; the Walls will stand forever. It becomes up to Grace to save her city and save her species.