The Builders of Ember construct the city for those who will come to live there. When the construction of Ember is complete, the chief builder and the assistant builder discuss how the city’s forthcoming inhabitants will have to stay there for at least two centuries, perhaps a little longer. The chief builder leaves instructions in a timed lockbox to help the future inhabitants know what to do when the time comes to leave Ember. Each mayor of Ember must guard the box, not knowing its contents, until the timer runs down and the box unlocks on its own.

Each successive mayor takes good care of the box, keeping it well hidden in the Gathering Hall and passing it secretly to the next mayor, until the seventh mayor. Sick with a coughing illness and surmising that the box holds a cure, he tries hammering the box open but fails. He hides the box deep in a closet in his home and dies before he can tell his successor about it: “There it sat, unnoticed, year after year, until its time arrived, and the lock quietly clicked open” (3).