Lina and Doon's village are having a rough winter. There is little food and water.
Lina and Doon find a book with their old city name on it. They decide to go back to find out what was going on.
They go to the hole where they can see the city and see a light in the middle of the city. Doon goes down to investigate.
Doon goes to the underground city to be met by a family. He gets kidnapped by them and they give him a lecture about how dangerous the outside world is. He later escapes.
When doon gets out of the cave he meets up with Lina and wraps the diamond, that he took from the city, in a cloth.
When they are trying to go back to the town of sparks, they get attacked by wolves. (They survive.)
Lina and Doon search the area more and they find a panel on a wall. They open it and find rows of diamonds.
Later: The people of sparks figure out how to make things like lightbulbs.