Mike Sweeney has been promoted to a new position as Homicide Detective. His family has been split by serial killer Ray Prager, who is in lockdown after killing two women and traumatizing (possibly raped) Mike's daughter, Sadie. Meanwhile, at work, Mike is assigned a case of a possible homicide of a baby and takes it to forensic psychiatrist, Pen Verrity to help him understand how the murder happened.

Detective Sweeney comes under suspicion of police brutality. Meanwhile a new case keeps him busy while he struggles to help Sadie prepare for the coming trial. Doctor Verrity tries to protect her son Mark from her husband and tries to deal with the death of their daughter. Audrey begins a relationship with another doctor and her not-yet ended relationship with Mike may cost her life.

Mike and Tom take a closer look into Bonnie Verrity's death against Roxy's orders. Meanwhile Pen and Jonathan Verrity's fight over custody of Mark comes to a head. Sadie worries about testifying in Ray's upcoming trial and beings an investigation into her father when Ray tells her about an old secret about him.

New revelations into Bonnie's death are made as the investigation continues and both parents become suspects. Mike tries to stay professional while Pen draws him deeper into her web, and begins to behaves erratically and dangerously. Sadie's credibility becomes an issue when she is accused by boys from school, which may hurt her at Ray's trial. Ray Jr. learns what made his father so unstable and gets news from his mother.

With three murder investigations on his plate, and his family in turmoil, Mike attempts to keep his head about him. Sadies investigation into Lissies death turns up some startling evidence causing her to doubt her own father. Rays friends go to extreme measures to help him. Pen continues to lose her mind, leading to potentially deadly consequences.

Things come to a head for everyone in Durham County. Mike tries to convince his daughter that he did not murder Lissie; Pen tries to convince Mike that she did not drown her daughter; Ray tries to convince Pen that he is not a murderer. Ray Jr. and Sadie butt heads over Rays trial. Audrey tries to reconnect her family. Tom tries to continue the investigations despite Mike and Glenns efforts to cover themselves. Jonathan awaits the return of his son from his potentially murderess wife. Some will cry and some will die in the shocking season finale.