American Monsters. The Demon Road trilogy, book 3

The epic conclusion in the mind-blowing supernatural thriller from bestselling author Derek Landy, creator of international sensation Skulduggery Pleasant.
Bigger, meaner, stronger, Amber closes in on her murderous parents as they make one last desperate play for power. Her own last hopes of salvation, however, rest beyond vengeance, beyond the abominable killers - living and dead - that she and Milo will have to face.
For Amber's future lies in her family's past, in the brother and sister she never knew, and the horrors beyond imagining that befell them.