It’s been several months since Lina and Doon escaped the dying city of Ember and, along with the rest of their people, joined the town of Sparks. Now, struggling through the harsh winter aboveground, they find an unusual book. Torn up and missing most of its pages, it alludes to a mysterious device from before the Disaster, which they believe is still in Ember. Together, Lina and Doon must go back underground to retrieve what was lost and bring light to a dark world.
In the fourth Book of Ember, bestselling author Jeanne DuPrau juxtaposes yet another action-packed adventure with powerful themes about hope, learning, and the search for truth.

From the Hardcover edition.

Nine months have passed since Lina, Doon, and their fellow Emberites left their underground home and joined the people of Sparks. Although the initial hostilities and arguments are over, life is still filled with hardships, and "Doon could see no way to make things better." Then one day a roamer appears and Doon trades for a mysterious book with only eight pages remaining; a book clearly marked for the people of Ember! Convinced that help of some kind can be found back in Ember, Doon and Lina sneak away and make the perilous journey together. Once there, Doon is captured and held prisoner by a family living off the supplies left behind. The father shows Doon a breathtaking blue diamond, which Doon takes with him when he escapes, certain that it holds the key to everyone's survival. This fourth and final title in the deservedly popular "Book of Ember" series is an exciting and satisfying conclusion. DuPrau has also given enough exposition so that a newcomer could enjoy it as a stand-alone. Lina and Doon are wonderful heroes. As the author points out, they "used the ordinary powers of courage... kindness... curiosity and knowledge." Because they use these powers, rather than supernatural ones, they are characters we can all identify with and root for. This story is ultimately one of hope—and every one of us needs that. Reviewer: Naomi Milliner