Dexter hasn't been in touch with Deb for months. She is off working on minor cases undercover and enjoying the escape. A body is found with a piece of the brain missing and a psychologist Dr. Evelyn Vogel offers Miami Metro her help. She seems particularly interested in Dexter.
Dr Vogel tells Dexter about how she helped Harry construct the Code. Then she asks him to protect her from one of her patients who is sending her the brain parts. While he is investigating that he has to deal with the murder of El Sapo who was shot shortly after beating up Deb. Meanwhile Batista tells Quinn to earn his respect by taking the Sergeant's exam.
Deb is arrested on a DUI and calls Quinn for help. He tells Dexter who tries to convince Deb that she has done a huge amount of good. Deb can't be shaken though and gets drunk again before marching into Miami Metro to confess to killing LaGuerta. Meanwhile Vogel gets more gifts from the killer who now knows that Dexter is involved.
Dexter begins investigating another of Vogel's former patients. Yates seems normal until Dexter discovers his shoe collection and his secret basement. Vogel seems to be making a breakthrough with Deb when the latter accepts that she would always choose Dexter over LaGuerta. But she then watches a DVD of Harry's interviews around the time of his suicide. Quinn aces the Detectives exam but gets into a bar fight when some cops bad mouth Deb.
Deb and Dexter get councilling from Vogel on their car crash. Quinn finds a murder suspect but his witness is quickly paid off and Matthews tells him to back off. Vogel is kidnapped by Yates. Dexter gets out of the date Jamie set up for him and he Deb go searching for Yates.
Dexter and Quinn seperately follow Zach Hamilton. Dexter is sure that he is a killer. Quinn is equally convinced but motivated by losing out for the position of Sargeant. Deb agrees to help Elway catch his sister's boyfriend cheating on her. Masouka offers his daughter some money.
Dexter wakes up unharmed as does Deb. He tracks down Hannah and her new husband with help from Zach. He coaches patience while Zach gets antsy. Masouka visits his daughter at work. Dexter helps Hannah with her husband who is controlling.
Dexter drives to the Keys with Hannah to look for Zach and kill him. However Zach didn't kill Cassie and is stalking a killer instead. Dexter takes his surrogate family to dinner at Dr Vogel's while Deb finds them but washes her hands of them. Masouka's daughter begins work in the lab and Quinn continues his investigation.
Dexter finds a DNA match at Zach's studio and it seems to be a relative of Dr Vogel's. She realises that it must be her psychopath son Daniel. Dexter lures him to a cafe but Daniel evades him. Deb investigates Daniel's alter ego with Quinn who kisses her.
Dexter tells Batista that he is leaving. Marshal Clayton finds out and gets suspicious. Quinn breaks up with Jamie and kisses Deb again. Dr Vogel tries to help Daniel but Dexter won't leave them alone. He thinks Daniel remains a threat and asks her to help him kill her son.
Saxon offers Dexter a truce but threatens his family as well. Dexter tries to sell his apartment and his boat. Dexter finds Saxon's kill room and his laptop with evidence which will put him behind bars. Marshal Clayton and Elway close in on Hannah McKay.
Dexter helps Hannah escape from Elway at the airport. Hannah and Harrison make their way to Rio while Dexter stays to take care of Saxon. Saxon is caught outside Deb's room but Deb suffers a stroke. Dexter kills Saxon.