The seventh season of Dexter premiered on September 30, 2012. The season follows Dexter's tangles with a Ukrainian mob boss and introduces the character Hannah McKay, a mysterious widow with a green thumb and a checkered past. The season seven story arc is continued over the course of the eighth season, which premiered on June 30, 2013.
After witnessing her brother kill Travis Marshall, Debra (Jennifer Carpenter) attempts to reconcile with Dexter (Michael C. Hall) while struggling to cover up their involvement with the murder. Meanwhile, Detective Mike Anderson has an unfortunate run-in, Quinn and Batista begin to make amends, and LaGuerta finds evidence that causes her to re-think the closed Bay Harbor Butcher case.
When a local convict claims he has new information regarding a 15-year-old crime spree, Miami Metro sets out to unearth new evidence on the case. Debra attempts to cure Dexter of his killer tendencies. Meanwhile, the Mike Anderson case leads to the Ukrainian mob and a vengeful Louis won't stop meddling with Dexter's life.
Dexter tries to bring Debra on board with his new target. While the Ukrainian mob seeks revenge for the killing of one of their own, Quinn grows close to a dancer at their strip club. LaGuerta, convinced the Bay Harbor Butcher is still out there, attempts to enlist Batista to help her re-open the case.
After capturing a deadly killer, things go awry for Miami Metro, sending Debra into a tailspin. In an effort to help his sister, Dexter enters into a dangerous game of cat and mouse, while the Ukrainian mob continues to seek revenge.
While trying to uncover why someone was killed on his boat, Dexter must out-maneuver a vengeful Isaak. New leads are brought to light on the Wayne Randall case by Hannah McKay, Randall's alluring former accomplice who Dexter discovers has a secret.
Dexter continues to investigate Hannah McKay as he is convinced of her guilt. Hannah walks in while he is in her nursery, searching for evidence supporting his theory - and thereby confirming her guilt. On being confronted by her he makes up a lie that he wants to ask her out on a date. She rejects the offer and says she is just trying to do the right thing. At which point Dexter coaxes her to "do the wrong thing". She agrees to go out with him. Quinn returns the money he was offered by George Novikov in exchange for some favour, saying he is not for sale. Later George shows up at a restaurant where Quinn and Nadia were supposed to meet for dinner. George asks Quinn to remove the evidence linking Isaak to the crime scene. When Quinn refuses, George threatens to send Nadia to a sex club in Dubaï. Quinn agrees to remove the evidence in exchange for Nadia's freedom and a promise that Isaak, once out of the jail, will leave the country for good. Meanwhile, LaGuerta continues to probe into the Bay Harbour Butcher and has a theory about how all the five suspects relating to the Barrel Girls' case went missing suspiciously. She confides to Debra that it is possible that the Butcher might have got to them. Debra confronts Dexter with this information and in the conversation that follows finds out about Dexter's relationship with Lumen. Elsewhere, Sal Price (Santiago Cabrera) is an investigative writer who has written a book on the life story of Wayne Randall. He thinks Hannah McKay might be more involved in the killings than previously presumed, and wants to write a sequel about her. To further his personal investigation into the subject, he approaches Miami Metro hoping to lay his hands on the case files. While on a date with him later, Debra finds out about the differences in the blood reports submitted by Price's guy and Dexter. This makes her suspicious of her brother again. Dexter and Hannah go to a closed Christmas-themed amusement park, where it turns out Dexter has a kill room set up. He prepares to kill Hannah, but cannot go through with it and releases her. They end up having sex in the kill room instead.
Hannah grabs one of his knives and holds it to Dexter's throat. She asks why he wanted to kill her. He says "it's what I do." Meanwhile, at Debra's house, Sal Price suggests exhuming the body of Hannah's husband to see if he might have been poisoned. The next day, Dexter drops off Hannah at her home but is spotted by Price. He confronts Dexter in the street telling him he knows Dexter fudged the blood reports. Dexter manages to convince Price not to say anything in exchange for information on Wayne Randall. Masuka discovers that the blood evidence used to arrest Issak is missing. Dexter, Masuka, Quinn and Angel go to the crime scene to look for more blood but the building has been flooded with sewage, destroying any possible evidence. They are forced to release Isaak, but Debra assigns a squad car to follow him around. Price visits Hannah at work and tries to get an interview with her. He threatens to go public with her relationship with Dexter unless she agrees. She agrees to the interview on the condition that he keeps Dexter out of his book. Dexter plans to incriminate Price in the murder of Christy Lawson, whose killer was never found. After exhuming the body of Hannah's husband, Debra discovers that he was never embalmed, and therefore there is no way to test for poison. Price interviews Hannah, who admits to stabbing the woman at the hotel. Later that night, Price goes to Dexter's apartment to find out what he knows about Wayne Randall. Dexter confronts Price with his plan to frame him for murder unless he backs off, but Price collapses and dies, apparently from a heart attack. Debra brings Hannah in for questioning over Price's death but is unable to get a confession. Later, blood tests come in negative for anything poisonous so she is forced to let Hannah go. Dexter visits Hannah the next night and stays over. Dexter receives a call from Deb asking him to do to Hannah what Dexter does best.
Dexter refuses Debra's request to kill Hannah, telling her she would not be able to live with herself if she ordered a murder. In reality, Dexter can't bring himself to kill Hannah because he's romantically involved with her. Meanwhile, Isaak shakes his police tail and tries to kill Dexter in a donut shop, but fails. Dexter sends Jamie to fetch Astor, Cody and Harrison from Orlando, since their grandfather is undergoing emergency surgery and their grandmother has to be with him. Due to Isaak's threat, Debra agrees to let the kids stay at her house. Angel buys Papa's Cafe. Deb later visits Hannah to assure her she's going to make her sorry. George tells his bosses in Kiev that Isaak has become too obsessed with avenging Viktor's death and is preventing the brotherhood from moving narcotics and laundered money. Dexter goes to Isaak's apartment to kill him, but finds a hitman already there, and ends up killing him. LaGuerta learns that Dexter moved his boat in May 2007, during the Bay Harbor Butcher investigation. Astor and Cody are fighting, and Cody reveals his sister smokes pot. Later, Deb agrees with Dexter's reasoning about not killing Hannah. Dexter runs to Hannah's house, where they talk about Dexter's need to kill Isaak, and they have sex. George uses a recording of their earlier agreement to blackmail Quinn into helping the Koshkas. Isaak finds the dead hitman and realizes he no longer has the protection of the Koshkas. Hannah needs to see Dexter while he's at the beach with his kids and ends up learning about them. Later, Deb sees Dexter has Hannah's keyholder and correctly deduces he's involved with her. Feeling hurt, betrayed and angry, she ends up confessing she's in love with him. Dexter does not know what to say. Afterwards, he follows Isaak to a gay bar, where Isaak tells him that Viktor was his lover, and they talk about what love is. Finally, Quinn is watching over a shipment from the Koshkas while LaGuerta finds Dexter's boat, Deb and Astor share a joint and Dexter goes back to Hannah.
Dexter takes Hannah on a boat ride only to discover she is terrified of water, the result of having been thrown into a lake by her father when she was six years old. This discovery prompts a discussion about one another's experiences regarding fear. Dexter is summoned to a crime scene where a man burned to death in his car. An assertive arson investigator rules suicide but Dexter thinks differently. When Dexter attempts to voice his opinion, the arson investigator briskly dismisses his theory. Dexter attempts to smooth things out with Deb by telling her he understands why she confessed her true feelings, reassuring her that the feelings are "logical". Meanwhile at the Koshkas' club, George is becoming increasingly agitated at Quinn's failure to return his calls. Out of spite, he forces Nadia to join him at a motel for sex. Elsewhere, Isaak discovers that the Koshkas have deployed two highly skilled hitmen to kill him. Desperate to save his life, Isaak approaches Dexter for help, which Dexter refuses. Back at the Koshkas' club, Quinn visits Nadia and learns that George assaulted her. He responds by fighting George and dragging Nadia from the club. Arriving home, Dexter finds Hannah's van outside and expects to find her. Instead he finds Isaak, who informs him that Hannah has been abducted and will be murdered if Dexter does not help him take care of the killers that the Koshkas have deployed. Seeing that Hannah is alive and being held by Jurg, Dexter relents and, after learning of the killers' habits from Isaak, tracks one of the killers to a shooting range where Dexter kills him. Dexter then demands to speak to Hannah before helping any further, and Isaak allows him to chat via video with Hannah. During the conversation, Dexter takes a screenshot and sends it to his cellphone. Later, after determining Hannah's location to be the residence of a Colombian, Dexter asks Deb to check out the Colombian cartel victims' houses from Isaak's previous killing spree. Meanwhile, LaGuerta meets with Matthews and admits she believes the Bay Harbor Butcher is still alive. She asks for Matthews' help, which he ultimately agrees to provide in exchange for his pension. When another burned body turns up in an elevator shaft, Dexter finds evidence that indicates it was not suicide and points out his findings to the visibly nervous arson investigator. Noting that the second hitman hunting Isaak had followed him to the crime scene, Dexter leads him to a ship where Isaak kills him. At the same time, Hannah attempts escape and strikes Jurg in the head but not before being stabbed in the abdomen. Back on the ship, Isaak and Dexter appear to make amends. As Isaak is leaving the ship, he is confronted by George who shoots him and flees. Dexter attempts to help him, but Isaak notes that the bullet did not exit and states that he is dying. As Dexter takes a dying Isaak out on his boat, Deb discovers Hannah's unconscious body at the Colombian victim's home and, setting aside her disdain for Hannah, calls an ambulance.
The department is called to another murder by the Phantom Arsonist, and Dexter's suspicion initially falls upon the fire service investigator himself. Hannah's father, Clint McKay, pays her an unexpected visit, having spent time in prison. The meeting seems congenial at first, but McKay soon turns nasty when Hannah refuses his request for $20,000 to open a business (actually, to pay off his gambling debts), using threats of exposing her for a past murder. Dexter tracks down the fire investigator's SUV at a park and notices all kinds of fire-starting equipment in it. When confronted by the fire investigator, Dexter realizes that he is not the arsonist, but only a Civil War reenactor. Dexter identifies the real arsonist, Joseph Jensen, when he runs his fingerprints through juvenile records. He initially planned to kill the arsonist himself but, instead, he hands him over to the police department anonymously. At the Koshkas' club with Angel Batista, Quinn hears that his girlfriend Nadia is being sent to a sex club in the Middle East and witnesses George physically assaulting her. He shoots George dead, then falsifies an alibi by claiming that George first shot him by having Nadia shoot him in the arm. Batista is not convinced, but he agrees to let Quinn tell his story. LaGuerta and Matthews visit the site of Doakes' death and discover a further connection between the Bay Harbor murders and Dexter. The program ends with Dexter killing Hannah's father, an event he keeps secret from her, but it is also revealed that the father had already leaked information to Dexter's sister Debra about Hannah's murderous ways.
Dexter attends the parole hearing of Hector Estrada, the last surviving killer of Dexter's mother, which leads to Estrada's release. Nadia is missing — Quinn later learns she has moved to Las Vegas. Angel Batista finds Arlene Schram, the witness to Hannah McKay's murder of the halfway house counselor she encountered after leaving juvenile detention. Dexter meets with Matthews on Matthews' boat. Matthews warns Dexter that LaGuerta thinks that he might be the Bay Harbor Butcher and tells him that they found the connection between Dexter and Jimenez. Dexter tells Matthews that Doakes owned a boat that he kept in the same marina Dexter used. Debra meets with Arlene and offers her a deal to avoid being made an accessory to Hannah's murder and Arlene goes to Hannah to speak with her about it. It is revealed that the counselor had been sexually abusing the girls. Matthews and LaGuerta visit a boat house in which Dexter and Debra had planted evidence incriminating Doakes, but LaGuerta is still not convinced. Dexter poses as a drug dealer to set up a meeting with Estrada. He then receives news his sister was involved in an automobile accident on her way to a second meeting with Arlene. Dexter suspects Hannah poisoned her. Dexter questions Hannah, who denies involvement in Deb's overdose. He later discovers Debra's water bottle contained a high percentage of Alprazolam, an anti-anxiety prescription drug Debra had been taking, leading him to believe Hannah had attempted to kill his sister. Dexter goes to kill Estrada but discovers he's been set up and that LaGuerta pushed for Estrada's release in order to catch Dexter in the act of killing him. Both Dexter and Estrada escape undetected. Dexter gives Debra evidence incriminating Hannah for Sal Price's murder. Debra has Hannah arrested for the murder of Sal Price.
As LaGuerta closes in on Dexter's secret, Dexter struggles to protect himself, Debra and the life he's built.