The Diamond of Darkhold is a post-apocalyptic science fiction novel written by Jeanne Duprau that was published in 2008. The novel is the fourth and final "Book of Ember" and was released on August 26, 2008. The fourth book picks up where The People of Sparks left off, during the Emberites' first winter above ground. Lina and Doon find a mysterious book that alludes to a mysterious device that was left outside Ember. An advance copy was given out to attendees of the San Diego Comic-Con 2008 who visited the Random House booth.