The next killer that Dexter goes after on Vogel’s list is a man named A.J. Yates who was placed in a mental health hospital when he was 15 years of age. Vogel tried desperately to channel Yate’s tendencies as much as she had with Dexter yet was unable to do so and ultimately failed in reforming him. When Dexter comes in contact with Yates, he notices a large scar on his forehead. He is later informed by Vogel that Yates had surgery to remove a brain lesion. Dexter breaks into Yate’s house and finds something of interest within Yate’s closet. Dexter is not alone in the house and it looks like he may be the man they are looking for. Dexter also finds something that will put a strain on his relationship with Vogel. Dexter meets a neighbor of Yates, named Cassie. The police have a victim, Norma Rivera, who Dexter believes was killed by someone close to her or by someone that she knew. Angel demands that Quinn, who has passed his exams, get down and solve this murder case if Quinn ever wants to make the Sergeant position in his police career. Masuka gets an unannounced visitor at the police station. Vogel begins her work with Deb trying to help her with her Post Traumatic Stress Disorder and they go and visit the very container in which Deb shot down LaGuerta. It seems as though Deb is making progress, but then doubt sets in.
The Brain Surgeon re-creates the crime scene where he slaughtered Sussman, placing his life less corpse on a meat hook, so that it looks like Sussman blew his brains out with a shotgun. This leads the police to think that it was Sussman who was the Brain Surgeon and killed himself out of repentance. He then sends pieces of Sussman’s brain, the optical portion, to Vogel labeled “His” and “Hers” letting Vogel and Dexter know that he is watching the both of them. Dexter proceeds to go through a list of Vogel’s ex-patients and comes across Ron Galuzzo, who had murdered his best friend when he was a child, but originally convinced Vogel that it was a bully who committed the crime. Yet this turns into a cold lead when they find out that Galuzzo is a cannibal. Meanwhile, Debra gets pulled over for a DUI, but Quinn helps her get out of it. Debra then proceeds to head to the police station with confessing to LaGuerta’s murder. Quinn calls Dexter and tells him what his sister is about to do. He and Vogel make haste to the police station to stop Debra and try to convince her that she is having survivor’s guilt. Dexter finds Debra within the interview room and when she tries to leave to make a public confession, he injects her with M99. Dexter then takes Debra home and asks Vogel to help her with her problems. At the conclusion of the episode, Dexter kills Galuzzo, calling him ‘Disgusting’ for being a man eater, even though he admits that the two of them are quite alike.
Dr. Vogel appears on Dexter’s door step and proceeds to show him a video tape she has that explains how she has the ability to know everything about him and where he came from. He finds out that it is in fact Dr. Vogel who had instructed Harry, Dexter’s father, towards teaching Dexter to funnel his murderous passion towards people who actually deserve it. She had developed the code, therefore developing Dexter. He does not look at her with fondness however, due to the fact that he has begun to hate his murderous urges at this stage and the lasting effect they have had on Debra. Vogel informs Dexter that the new murder in Miami is possibly one of her bygone patients. He thinks this because the murderer is putting samples of his victims brains in jars and leaving them on her doorstep. She feels deeply troubled by this and asks Dexter to take care of him for her. Dexter candidly refuses however. The Brain Surgeon in the meantime kills another victim with the help of a fall guy, and dumps the body. This time though, a fingerprint has been left at the crime scene. Unfortunately, this fingerprint in question belongs to Sussman, who was butchered by the Brain Surgeon and later framed for the crimes the Surgeon has committed. The Brain Surgeon then breaks into Vogel’s home and leaves her a DVD, containing the graphic and horrifying footage of him murdering Welks and Sussman. Both Dexter and Vogel come to the realization that this is truly happening all the while trying to keep it from Metro Police.
It has been six months after Debra has shot and killed Officer LaGuerta. A mentally-destroyed Debra has now quit her job at Miami Metro due to the immense amount of guilt and grief she has been feeling after killing her fellow officer. In her absence, Officer Batista comes out of retirement and is immediately promoted to the vacant position of Lieutenant. A new serial killer is on the loose out in Miami and is nicknamed the “Brain Surgeon” and Miami Metro is on his tail. Metro is getting some unexpected help from the psychopath expert Evelyn Vogel (played by Charlotte Rampling) who has quite the engrossment for Dexter. While this is all taking place, Debra is in the process of an undercover job with a private investigative company to bring in a bail jumper who has taken off with over $500,000 worth of jewelry that had been in a mob-controlled facility. Dexter finds out that the person Debra is trying to take down town is actually a mob hit man. Yet Dexter goes into a red rage after trying to discuss this with her and ends up killing the hit man’s mark, all the while the hit man secretly watches Debra leave. Quinn and Jamie have begun a relationship, which Quinn really wants to keep from Batista. Near the end of the episode, Dexter encounters Vogel who has murderous drawings from his childhood. Dexter threatens to kill her but she kindly reminds him that he can’t due to the fact that she does not meet Harry’s Code standards.