Dexter tells Deb that he fought Travis off and killed him in self defence. They burn the church down but she soon realises that he was lying. She looks into the Ice Truck killer files and begins to piece the truth together. Mike tries to help someone with a burst tyre and gets shot. The killer Victor escapes but Dexter is soon on his case. LaGuerta spots a blood slide at the church and begins to look into it.
Deb is distraught to find out the truth. She insists that Dexter move in with her so she can keep an eye on him. He agrees but wants to find out why Louis sent him the prosthetic from the Ice Truck Killer case. He manages to sneak out on an assignment while she focusses on Mike's murder. Meanwhile LaGuerta continues her investigation and Quinn becomes friendly with one of the strippers at the Fox Hole.
Dexter is feeling suffocated by Deb's attention. He asks her to back off and uses the space to hunt Ray Speltzer, a man who has murdered two girls but evaded arrest. Dexter tells Deb about what he is doing and she is torn. Nadia is told to get close to Quinn and confides in him how dangerous her bosses are. Dexter gets Louis fired and to gain revenge he tries to sink the "Slice of Life." But he is caught there by Isaac who kills him.
Speltzer is brought in for questioning and admits to killing the girl. Deb is disturbed by thoughts of how Dexter was responsible for Rita's murder and what life Harrison is being given. When Speltzer is released on a technicality Dexter goes after him and is knocked out. He wakes up in one of Speltzer's mazes and escapes. Meanwhile Isaac forces the bartender at his club to commit suicide to get the police off his back.
Isaac lies in wait for Dexter and the two admit they are now trying to kill the other. Dexter leads Isaac into a rival gang's bar but Isaac kills three men and survives. He is arrested but tells Dexter that their blood feud isn't over. Hannah helps Miami Metro find the bodies she was involved in burying. Dexter can tell she killed people but she has immunity from prosecution. Deb is shocked to learn that Dexter killed Victor and ends up obstructing both Batista and LaGuerta from continuing investigations which might catch Dexter. Isaac suggests they try to bribe Quinn who takes the money left in his car.
Dexter and Hannah keep making excuses to see each other as he tries to find out if she is still a killer. Deb goes on a date with Sal Price, the man who wrote the book about Wayne and Hannah's killing spree. He now thinks that Hannah was involved in murdering people. LaGuerta focusses on the Jordan Chase murders in case the Bay Harbour Butcher was responsible for them. Isaac asks George to get him out of prison. George threatens Nadia and bribes Quinn to get him to tamper with evidence.
Hannah and Dexter agree that it was a one time thing but begin covering for one another with Sal Price. She gives him some of her story and then poisons him. His next appointment is at Dexter's where he falls down dead. Deb is furious and accuses Hannah of killing him. Meanwhile Isaac is released and vows to kill Dexter despite the police officers following him around. Quinn assures Nadia that all will be well and gives his ill gotten money to Batista for his restaurant. LaGuerta finds some evidence linking Dexter to the Bay Harbour Butcher case.
Isaac takes a shot at Dexter while he is buying doughnuts and so Dexter heads to Victor's apartment to kill him. Meanwhile George turns Isaac into the rest of the Brotherhood and an assasin is waiting in Isaac's apartment. Dexter kills him and then follows Isaac to a gay bar where he learns the truth about Isaac's relationship with Victor. Meanwhile Dexter increasingly wonders if Hannah could be part of his family. Astor, Cody and Harrison return to his care as their Grandfather needs to go to hospital. When Deb finds out about Hannah she flips out and admits that she loves him. George reveals to Quinn that he taped their conversation and LaGuerta zeroes in on Dexter.
Isaac kidnaps Hannah and forces Dexter to kill the assasins sent after him. George forces Nadia to sleep with him to send a message to Quinn. George also kills Isaac when the assasins fail. Deb finds Hannah who managed to kill Jurg. A new killer appears on the scene burning his victims alive.
Hannah's father Clint arrives to apologise for being a bad father. He soon reveals his true colours and his desire for cash. Hannah wants to pay him but Dexter has other ideas. Meanwhile Dexter questions whether he has a dark passenger and catches the fire starting killer. Quinn kills George and claims self defence while LaGuerta and Matthews close in on Dexter.
Deb tracks down Arlene and threatens her in order to get her to testify against Hannah. Hannah confronts Deb and soon Deb falls asleep at the wheel. Dexter is disturbed by the thought that she could have poisoned Deb. Meanwhile he is distracted by Matthews telling him about LaGuerta's suspicions and the release of his mother's murderer Hector Estrada.
LaGuerta arrests Dexter for the murder of Hector Estrada but he planted evidence which makes her look like a fool. He jumps back on Estrada's tail while Hannah makes arrangements to escape prison. Batista and Matthews urge LaGuerta to drop the case but she uncovers new evidence which incriminates Deb.