Diamond of darkhold - book of ember 4

Lina and Doon are returning to the city of Ember, but what awaits them in the dark? This highly acclaimed adventure series is a modern-day classic—with over 4 MILLION copies sold!
 
Lina and Doon escaped the dying city of Ember and led their people to the town of Sparks. But it’s winter now, and the harsh realities of their new world have begun to set in. When Doon finds a book that hints at an important, long-lost device, it doesn’t take much for him to convince Lina to join him for one last adventure in the place they used to call home. But will this mysterious technology be enough to help their people? And what— and who—will they find when they return? 

Praise for the City of Ember books:
 
Nominated to 28 State Award Lists!
An American Library Association Notable Children’s Book
A New York Public Library 100 Titles for Reading and Sharing Selection
A Kirkus Reviews Editors’ Choice
A Child Magazine Best Children’s Book
A Mark Twain Award Winner
A William Allen White Children’s Book Award Winner
 
“A realistic post-apocalyptic world. DuPrau’s book leaves Doon and Lina on the verge of undiscovered country and readers wanting more.” —USA Today
 
“An electric debut.” —Publishers Weekly, Starred
 
“While Ember is colorless and dark, the book itself is rich with description.” —VOYA, Starred
 
“A harrowing journey into the unknown, and cryptic messages for readers to decipher.” —Kirkus Reviews, Starred