The Silent Wife by Karin Slaughter

 I didn't realize this was part of a long-running series so I didn't know the whole backstory with Sara and Jeffrey then Sara and Will. But I figured it out as I went along, so that didn't matter so much.

But let me just warn you that this is a very violent book. GBI agents Will and Faith are hunting a man who stalks, drugs, paralyzes, rapes, then leaves women for dead. Over and over. And we hear about it in great detail. After a while, I had to start skimming over the gory details because it was too much. 

I did have an inkling of who the bad guy was way before the end. If you pay close attention, you may be able to figure it out too.

The only parts of this story that I really liked were the Sara/Will love story and the Faith/Will professional partnership. Not sure whether I would read more of this series if they're all this violent.