The Running Grave by Robert Galbraith

 This is the latest in the Strike and Robin series featuring 2 London PIs who are in love with each other but won't admit it. In this volume. Robin goes undercover at a religious cult out in the countryside to get the dirt on the cult and try to free one of the members (the son of their client). In the process she faces rape, corporal punishment, a starvation diet, sleep deprivation, and the feeling that she might be losing her mind. So it's not exactly a cheery little read At the same time, Strike's obsessive ex, Charlotte, keeps popping up. Someone is stalking the agency. And they may have a mole in their midst. Plus Strike's beloved uncle is developing health issues.

I like this (very long) book better than the one before it (equally long, with an impossible-to-untangle plot). And I'm glad to see that Strike and Robin might finally be acknowledging how much they mean to each other. But make sure you have plenty of time to devote to this book because it is very long.