After what he saw, Dexter finds it impossible to resume his secret life and decides to abandon his principles. Debra, on the other hand, goes back to work but is still dealing with the aftermath of the incident.
Dexter continues to stalk a dangerous new victim, and Debra loses control of herself while working. An agent arrives in Miami to investigate the case of a new serial killer.
Dexter fails to lie, so he chooses a skilled liar to become his next victim. Rita believes that he is addicted to drugs and forces him to join a rehabilitation program where he meets a woman named Lilia.
Rita feels threatened by Dexter's new relationship and receives a visit from her long-absent mother. Elsewhere, Dexter tries to escape the constant persecution of Detective Lundy.
Dexter decides to go meet the man who killed his mother after learning that he is still alive, but he soon finds that the reasons behind the murder are still hidden within him.
A new murderer appears who adopts the same way as the Bay Harbor Butcher, a serial killer. When Dexter needs help again, he turns to Lila for comfort and as their relationship grows, Dexter breaks up with Rita.
Dexter's scheme to put Lundy off his trail includes a written statement from the "Bay Harbor Butcher" that throws the task group responsible for arresting him into a state of chaos.
Dexter makes the decision not to finish his therapy. In addition, he goes to visit his mother's killer again.Lundy and Debra discover proof that the "Bay Harbor Butcher" may be closer to them than they had previously thought.
Dexter tries to get away from Lila, but she refuses to give up on him, before Detective Landy's pursuit makes him worry, and one of his worst enemies discovers a secret about him, which puts him in trouble.
As Miami police get closer to catching the "Bay Harbor Butcher," Dexter's world suddenly crashes when Sergeant James Doakes tracks him to the location of his most recent murder.
Dexter is exposed to real danger and is forced to make difficult decisions about the people he cares about. Lila tries to blackmail Dexter and makes a shocking discovery about his secret life.
Finally, Lundy and the FBI crack the case of the "Bay Harbor Butcher," but Dexter must rise once again from danger, facing a true disaster.