Search - The Diamond of Darkhold: The Fourth Book of Ember

This is the fourth installment of the City of Ember series. I really liked City of Ember, but haven't liked any of the sequel/prequels as much.

Lina, Doon and the Town of Sparks are sturggling to survive a harsh winter. Lina and Doon decide to go back to Ember to find leftover food, medicine and a mysterious item the founders thought would be helpful to the emerging people of Ember.