Dark Places, by Gillian Flynn, begins with the main character, Libby Day, talking about her life. Several members in Libby’s family were murdered when she was only 7 years old. To make matters worse, the killer was her older brother, Ben. Libby has been living off inheritance money and all the funds that were raised to help take care of her after the murders. Now Libby is running out of money and doesn’t have any serviceable skills. She’s approached by someone named Lyle, who runs what he calls a Kill Club.

The Kill Club is a group that’s obsessed with studying crimes and criminals. They’re fascinated with Libby because many of the members believe that Ben is innocent. Lyle is willing to pay Libby to speak with them, and she agrees because she needs the money. The club members bring up a lot of details the cops either missed or ignored, pointing out that her testimony was forced given that she didn’t actually see any of the murders. It didn’t help that during the 80’s everyone was afraid of satanic cults. Supposedly, Ben committed the murders because he was part of such a cult.

At first, Libby doesn’t believe them; but, she needs to keep seeing the group because they’re paying her. After a few more visits, she finally gets the courage to see her brother in prison, something she had never done. After speaking with him, she starts to accept that he wasn’t the killer, but she knows he’s holding something back.

The story switches between Libby’s investigation in the present and what happened on the night in 1985 leading up to the murders. This section explores the dysfunctional family relationships that Libby had. Her family was incredibly poor, and they practically grew up without Runner, their father. Runner only showed up whenever he needed money. When he did show up, he was cruel to the family. Ben was struggling at school and felt like he didn’t belong in the world. He was upset and angry. His only real friend was his girlfriend, Diondra. Even Diondra treated him like a second class citizen, as did her friend, Trey, who was frequently around them.

A younger student, Krissi, has a crush on Ben when he volunteers at her class. She spreads rumors that she and Ben had gotten physical, which leads to more girls coming forward with their own stories. These lies continue to escalate, and Ben is suspected of being a child molester. These rumors evolve further, leading to Ben being part of a Satan worshiping cult. To make matters worse, this all happens while Ben is dealing with an unexpected pregnancy from Diondra. On top of that, his mother, Patty is about to lose the farm.

In the present, Libby is slowly able to piece together what happened. She finds out about Diondra and manages to track her down. She meets not only Diondra, but her and Ben’s child, Crystal. Crystal lets it slip that Diondra murdered one of Libby’s sisters because she knew about the pregnancy. They try to murder Libby, but she’s once again able to escape. With the help of Lyle, she’s able to uncover additional evidence about the crime.

She learns that Ben and Diondra were going to run away together to raise their child. They stopped at home to take whatever money they could get. At the same time, Patty had made a deal to arrange her own death. She knew she couldn’t care for her family, but if they had the insurance money from her passing they might have a chance. The murderer showed up at the same time as Ben and Diondra. Libby’s other sister got caught in the crossfire, along with Patty. Ben got blamed for everything because of his reputation in town. He stayed silent because he wanted to protect Diondra.

With everything they’ve learned, Libby and Lyle are able to present the new evidence to the police, and Ben is finally freed from prison. Ben doesn’t know what he wants to do with his life because he had been behind bars so long. He felt like the world was still against him. He’s determined to make things work with Libby’s help. Libby herself is finally able to move on from what happened that horrible night. By the end of the book she, too, is hopeful for the future.