When a roamer trades them an ancient book with only a few pages remaining, Lina and Doon return to Ember to seek the machine the book seems to describe in hopes that it will get their new community, Sparks, through the winter.

When Will Burrows and his friend Chester embark on a quest to find Will's archaeologist father, who has inexplicably disappeared, they are led to a labyrinthine world underneath London, full of sinister inhabitants with evil intentions toward "Topsoilers" like Will and his father.

Four generations ago, the Earth was rendered uninhabitable and those who remained were forced underground. In Compound Eleven, the hierarachy of floors is everything and on Eve Hamilton's floor, they fight. When she meets a boy from the top floor, Eve is no longer content to just survive, she is ready to fight for freedom.