Doakes follows Dexter to his next crime scene and shocks him with a revelation about Harry. The Bay Harbor Butcher task force feels they are zeroing in on their man.

Dexter has always known his father’s Code was meant to protect him from exposure. But after committing a serious mistake, he wonders if it could have been designed to protect him from something even more dangerous – human emotion. When he discovers that Trinity is planning an out-of-town trip, Dexter sees an opportunity to ride along and gain insight into the mind of a fellow monster.

Dexter and Arthur find themselves on a collision course, as Debra unearths a shocking long-hidden truth, Rita admits her marriage to Dexter is troubled, and Batista and LaGuerta face the consequences of an ethics breach.

Homicide uncovers some key evidence linked to one of Dexter's and Lumen's prior victims; Debra identifies two more suspects in the case.

With the help of his newfound friend Brother Sam, Dexter wonders if there is light within him to counter the darkness, while the search for the Doomsday Killers takes him in a new direction; Batista and Quinn pay a visit to the university where Professor Gellar taught; due to departmental regulations following the shooting, Debra is forced to begin therapy.

Dexter tries to figure out the Doomsday Killers' next victim before it's too late; Debra has a strong reaction to a crime scene, which leads her to the realization that she leans too heavily on her brother.

Dr. Vogel gets abducted by the Brain Surgeon, while Dexter and Debra try and rescue her. Masuka finds out he has a daughter.

Dexter enlists Dr. Vogel's help to lure the Brain Surgeon to a location in order to get him on the table. Later, an important person in Dexter's life is murdered before his eyes.