Libby's mother and two sisters were murdered when she was a young child, and her brother (Ben) has been in prison for the crime the last couple of decades. Driven by monetary gain, Libby, who's testimony helped incarcerate her brother all those years ago, starts to delve into the murder to determine if her brother really did it. 
 Much like Gone Girl, this title sucked me in and I lost some sleep in my desire to finish it. Also similar to that book, the ending for Dark Places let me down a bit. Beyond that, I like Flynn's writing, a lot. Her characterization shines, and I could easily picture all of those people in my head. Sure, most of them are not redeeming as humans, but I prefer complex characters with layered personalities over a sunshine-and-roses world where everyone is a goody-goody candidate for sainthood. 
 I also liked how the mystery developed slowly, through chapters that alternated their narrator, as well as the date. So, Libby in the present day might be one chapter, the next might be Ben on the day of the murders, and the one a few after that might be Patty (the mom) on the night of the murders. If you really like any of Flynn's novels, you'll probably like this.