The young protagonists, Lina Mayfleet and Doon Harrow, follow clues left behind by the original builders of the City of Ember, to safety in the outside world.

The Builders give the first mayor of the city a box with a timed lock set to open after 200 years, containing instructions explaining how to leave Ember.

Approximately two hundred and forty-one years after Ember was established, the city's supplies are in danger of exhaustion, and its hydroelectric generator is in decay, causing the power to go out intermittently.

At work, Doon discovers that the mayor of Ember and a storeroom worker named Looper have been stealing supplies, and he and Lina report the crime to the guards, who unknown to them, are also corrupt.

Kirkus Reviews praised the characters, stating: "The likable protagonists are not only courageous but also believably flawed by human pride, their weaknesses often complementing each other in interesting ways.

[4] Robert Sutton from Horn Book Magazine compared the novel to Gathering Blue by Lois Lowry, noting how "the darkness of Ember is essentially literal" with the generator (the mechanical light operator) failing and running out of power, leading to frequent blackouts.

Sutton noted how DuPrau does not explain the history of Ember all at once, which would confuse and overwhelm the reader and instead, "allows the events of the story to convey the necessary information".

[5] Dian Roback from Publishers Weekly also praised the "full blooded characters" as every bit as good as the plot which would hook readers until the end.

[6] Although Jones Johns from School Library Journal wrote that the setting was not as ingenious as the ones in Joan Aiken's Is and Lois Lowry's The Giver, he said that the characters and pace of the plot would keep readers hooked.

[7] A film adaptation of the novel, directed by Gil Kenan, was produced by Walden Media and Playtone with Bill Murray as the mayor, Saoirse Ronan as Lina, and Harry Treadaway as Doon.