The Treatment is essentially the next book in a series of, hopefully, many books following DI Jack Caffery (the first book being Birdman). This time, Jack is out to catch a killer that holds a family up in their house, chained to radiators, as he sodomizes the children in the family. The families aren't given any water, and the females are kept away, being labeled as a "hazard". Unfortunately, this case reminds Caffery of a case he was personally involved in when his brother, Ewan, was abducted as a child, never to be found again. We learned about Penderecki in Birdman, and we learn even more about him in this book.
As much as I enjoy Caffery as a character, I have found that Birdman and The Treatment are Hayder's weaker works. Not that they are bad by any measure. Really, I'm comparing the likes of Pig Island (a 10/10 book for me), and Tokyo (either a 9 or 10/10 book). Hayder is still an awesome author, and these books are great, they just aren't her best. When I read a Hayder, I expect to never see the ending coming. In this book, however, I could figure out who the murderer was and while there were a few surprises, this was a little disappointing. I was also alarmed at how quickly Jack found the name of the murderer after one small little clue. Maybe I didn't understand it correctly, but it seemed that they went through so much, then all the sudden this name pops out of thing air.
I can't remember if I liked Becky (Jack's girlfriend) in the Birdman, but this left me feeling like she was cold. Granted, she had been through a lot. I tried to give her a break but I really couldn't, and found that she wasn't a likable character.
Given how the book ended, there HAS to be another Caffery novel coming out and I'm looking forwards to it!!