Book ~ "The Watcher in the Wall" (2016) Owen Laukkanen

From Goodreads ~ Kirk Stevens and Carla Windermere of the joint BCA-FBI violent crime task force have handled shocking cases before but this one is different. 

Stevens’s daughter, Andrea, is distraught over a classmate’s suicide, but what the two investigators find is even more disturbing - an online suicide club of unhappy teenagers, presided over by an anonymous presence who seems to be spurring them on. Soon it becomes apparent that the classmate wasn’t the first victim - and won’t be the last, either, unless they can hunt down this psychopath once and for all.

Carla Windermere is an FBI agent and Kirk Stevens is a special agent with Minnesota's Bureau of Criminal Apprehension ... they work together on a joint FBI-BCA violent crimes task force.

Windermere and Stevens are wrapping up a case when Adrian, a classmate of Stevens' daughter, commits suicide.  Stevens checks it out and discovers the student had been the object of bullying ... this brings back memories and guilt for Windermere of when she was in high school and a fellow student went through the same thing.

Further investigation reveals Adrian was on a chat forum for people wanting to commit suicide and they discover that someone named Ashley had befriended him and encouraged him to take his life while she watched, saying that it would give her the courage to do the same.  They find that Adrian isn't the first person Ashley has encouraged to commit suicide while she watches.  Windermere and Stevens are determined to hunt her down before she can convince others to end their lives.

I liked the writing style and it kept me interested.  It's written in third person perspective with a focus on Windermere and Ashley.  As such, you get to know Windermere and Ashley well as the story jumps back and forth from the past to the present.  As a head's up, there is swearing.  I didn't find Windermere especially likeable ... she's so hard, cold and unfeeling and a bit messed up.

Though this is the fifth in the Stevens and Windermere series, it works as a stand alone.  I had read the first one when it came out in 2012.  I enjoyed it and said I could see them teaming up for a series and they have.  I'm going to go back and catch up on numbers two to four.