Hell Fire by Karin Fossum

Caregiver Bonnie Hayden, a single mother with a preschool son, Simon, is scraping by financially. When they are found viciously murdered in a neglected trailer, Inspector Sejer, wonders who might of wanted them dead, since Bonnie had no apparent enemies. The story of the investigation into the killings is alternated with the tale of the last six months of Bonnie's and Simon's lives. Fossum also adds a third storyline, that of loner Eddie Malthe, who lives with his mother, Mass. Eddie has a cruel streak and seems psychologically unstable. In Hell Fire, Fossum depicts the daily lives of these characters as they proceed to their shattering conclusions.  A heartbreaking tale of fate, love, and loss.