Dexter has decided that he wants to make a new life for himself with Hannah and Harrison but not before he has dealt with the murderous monster Brain Surgeon. While searching Zach Hamilton’s art studio, Dexter finds blood and a clump of hair underneath a desk. When Dexter takes it in and runs a DNA scan, he comes to find out that the blood belongs to someone who is related to Dr. Vogel. While quite skeptical of his findings he tells Vogel that the Brain Surgeon is somehow related to her. Vogel sits Dexter down and explains that she once had two sons. One of which, Daniel, killed his younger brother. He was placed in a mental institution but died from a fire in the institution when he was only 14. Dexter strongly believes that he survived and quickly has him singled out. Dexter tells Vogel that her son is still alive and Dexter plans on killing Daniel. She admits that she is a bit conflicted with this fact and tries to convince Dexter that Daniel needs a second chance. Dexter goes along with it and asks for assistance in finding him. He finds out that Daniel has been monitoring his mother on her laptop with spyware. Deb begins to have doubts and second thoughts about returning to Miami Metro Police. She has also allowed Hannah, who is now being hunted down by a Federal Marshal, to hide out at her house.
Dexter is quite certain that it was Zach who bludgeoned Cassie to death in her apartment. It seems as though it was an impulsive murder rather than planned out like Norma Riviera’s murder. Dexter comes to find out that it is Zach’s blood under her fingernails and does not report it to the police for obvious reasons. Dexter tries to keep the police off of Zach’s tail. Dexter and Vogel converse about how they can not find Zach and he blames her for Cassie’s death due to the fact she talked Dexter out of killing Zach. Zach ends up in the Florida Keys. Dexter finds this out because Zach has used his credit cards down there. Dexter and Hannah pack up to go and find him. What Dexter finds impresses him but also indicates that Zach is not the killer of Cassie. Dexter finds Zach dead with a large portion of his skull missing which indicates that it is the Brain Surgeon behind all the murders. Vogel is now in possession on a chunk of Zach’s brain, just like all the other victims. All the while, Dexter is in the process of helping Hannah obtain a new identity and making plans to get her out of the United States. Although during this process, Dexter begins to see that the bond he shares with Hannah is becoming quite strong and he begins to start seeing a different future for himself, possibly with Hannah in it.
After being unknowingly drugged by Hannah McKay, Dexter regains consciousness in an industrial zone just outside of Miami. He knows for certain that Hannah is responsible for this and she is oddly quite easy to find, which in turn increases Dexter’s growing suspicion. Turns out that Hannah is currently living in the lap of luxury on a yacht with her husband Jacob. She had changed her name to Maggie and confesses to Dexter that she is quite happy now with her new life and husband. Jacob isn’t quite happy knowing that she has met with Dexter and has asked Dexter to help her with her problems. Deb on the other hand tells Vogel that she wants Hannah to be placed under arrest but confesses to Vogel that she knows too much already. Meanwhile, Dexter has agreed to take Zach under his wing and teach him the ins and outs of the Code, much to Dr. Vogel’s pleasure, but he is turning out to be quite the difficult student to teach. Someone close to Dexter has been murdered in the same fashion that Norma was. Due to this fact Dexter is quite sure that it was Zach who committed the crime, he is uncertain whether he will be the kind of teacher that Harry was. Masuka goes out and helps arrange a new job for his daughter so she can finally get out of the financial hole she has put herself in.
Dexter is sure that it was Zach Hamilton who killed Norma Rivera but he has no solid evidence to really stand on and begins to follow Zach every chance that he gets. Dexter is therefore completely thrown off when he sees Zach enter Dr. Vogel’s office. Vogel admits that Zach Hamilton is a new patient of hers but refuses to talk to Dexter about his case. Batista is under a lot of pressure from Deputy Chief Tom Matthews about making a final decision on who he is going to promote to Sergeant and won’t get off his back until he makes a decision. When Quinn finds out the disappointing truth that he didn’t get the promotion he kicks it into overdrive to solve the Rivera murder case. With Dexter going along with Quinn, it becomes quite apparent to Dexter that Zach is in the process of stalking his next victim, Sofia Fuentes, a cute waitress who works at the country club at which Zach’s family has a membership. Meanwhile, Deb’s boss is on a hunt to prove that his sister’s boyfriend is cheating on her and is going after other women. Deb agrees to set up a sting operation on the man. Dexter heads out on a date with his next door neighbor Cassie. Masuka unfortunately finds out that his newfound daughter might be experiencing financial problems. Dexter begins to feel light headed and dizzy, and that’s when Hannah walks through the door.