Lina Mayfleet and Doon Harrow obtain the book via barter but soon learn it contains only eight pages, as the trader used the rest to light campfires.

Meanwhile, Lizzie Bisco (from Ember), Torren Crane, and Kenny Parton (both from Sparks) attempt to locate Lina and Doon but don't succeed, prompting another, larger search party to go looking for them.

Ultimately, the people of Sparks and the former Emberites help them retrieve the diamonds and other items left behind in Ember, enough to ensure both groups will survive the coming winter.

Lizzie takes an interest in Tim Troggs (abandoning her earlier hope of becoming Doon's girlfriend), while Lina gets a horse named Fleet and becomes a messenger like she was in Ember.

Many years later, after new cities have been built using solar power, one of their descendants views the now-fragile pictures drawn by Lina as a girl in Ember and notes how strongly they resemble a world she didn't live to see but nonetheless helped create.