Excellent audio book presentation of a tough topic. Two girls, abandoned by their mother, try to eke out a life in Cold Creek, Colorado. Sadie is the older sister, protective of Mattie, five years her junior. They live in a mobile home park and are looked after by the woman who manages the park. 
The audio book follows the story of a journalist who has learned of their story  - including Sadie's disappearance from Cold Creek. He sets out to learn about Sadie and Mattie in the hopes of finding Sadie. The second voice is Sadie herself as she travels Colorado and neighboring states looking for the man who lived with her mother for a while and who Sadie refers to as her father.