The Good Father - Noah Hawley
One of the most traumatic reading experiences I have ever had - and one of the most rewarding.

Who among us can say how we would react if someone we love committed an atrocity we despised?  The characters felt like people I knew, and I raged and grieved right along with them.  The only perspective to which I could not relate was that of the stepmother, whose motivations I questioned even as I struggled to accept that what she wanted was probably an appropriate outcome.