Like Diamonds in the Darkness: The Diamond of Darkhold: The City of Ember, Book 4 by Jeanne DuPrau
Lina was about to say goodbye to Doon, but he took hold of her arm. "Lina," he said, "look at this." There was something in his voice that made her turn to him in surprise. He held out the book, showing her the cover. "Directions for Use," it said in large print.
"Use of what?" said Lina. "I don't understand."
"No, look down here," said Doon, pointing at smaller print at the cover's lower edge.
Lina peered at it. "For the people of Em..." it said, and then there was a blot of something on the last part of the word. But it didn't matter. She knew what the word was. She looked up at Doon, wide-eyed.
"Ember," they both said, speaking at the same time.
It has been a few months since Lina Mayfleet and Doon Harrow found a way to lead the people of Ember out of the underground sanctuary where their ancestors had lived for over two centuries, surviving an apocalyptic war aboveground with the provisions and technology left by the prescient Builders of the City of Ember. But life on the surface is hard, and the small colony that forms the City of Sparks struggles to live in a second Dark Age where starvation and disease are ever present threats.
Then a Roamer, a traveling trader, visits Sparks, and in her wagon Doon spots the remnants of a large, ripped book. Maggs, the trader, has used most of its pages as fire starters and is happy to trade it for a few matches from Lina's precious cache from Ember. Although Doon and Lina can make little of the complex diagrams inside and terms like "joule" and "current," Doon convinces Lina that the book describes something important left for the people of Ember from the Builders and that they should return to Ember and search for this gift.
When the two make the difficult and dangerous trek back to the opening to Ember, they discover a strange glow from the deserted city underground. Descending down a treacherous, winding path, they make their way to the outskirts of the city, where Doon, running ahead, is suddenly captured by a band of squatters subsisting upon the leavings of the city. The Trogg family apparently discovered the same path and taking refuge from the bitter cold up above, are looting the items left behind for a summer trade expedition outside. Doon is shackled by their leader, who in a moment of braggadocio reveals his prize, a glittering blue and silver object he calls his "Diamond."
When Lina hears the sounds of Doon's capture, she flees back along the path and sets out to get help from Sparks, but as night falls outside, she meets up with the Roamer, who tells her of the beautiful and valuable "diamond" her brother Trogg is keeping to trade. Encouraged by Lina's interest in their prize, Maggs proudly leads her to the strange metal-clad room built into an outcropping in the mountain where the strange object and the book were found.
When Doon manages to steal Trogg's "diamond" and escape to Sparks, the two examine it carefully and discover that its base has a socket into which light bulbs brought from Ember seem to fit. At first the bulb remains dark, until Doon discovers that it glows brightly if the diamond is left outside in the sun. Returning to the metal room, Lina discovers a hidden panel which opens to reveal a thousand of the silver and blue solar energy cells--the final gift from the Builders to the people of Ember.
Book Four of this series is an engrossing adventure which puts main characters Doon and Lina back together in a quest at the very thematic center of the series. The closing lines of The Diamond of Darkhold: The Fourth Book of Ember (Books of Ember) satisfyingly ties all four books together with a powerful symbol and a message of hope:
But the spacecraft continued its journey, and those who had sent it continue to monitor its progress over the many decades of its flight. Finally, a few months before Lina and Doon made their trip back to Ember, it arrived. It has been collecting data to send back to its home planet. It will report that the magnificent and powerful civilization it had expected to find seems to have disappeared and that a smaller and much humbler one has taken its place.
It will observe that a great part of this world lies in darkness during the night, but not all. In some places, sparks of light shine--not fires but electric lights, bright gleaming spots like diamonds in the darkness.
The people here seem not to have lost everything that came before, the little craft will report. Some of them have survived; some of their learning, too. It seems clear that they are making a new start.
Walden Media's movie The City of Ember opens October 8. You can see its trailer and other promotional information here.
For more about the Ember series, see my review of The City of Ember (The First Book of Ember), posted on July 31 of this year.