Dexter Morgan, a Miami Metro Police Department blood spatter analyst, is living a double life. After his day job with the police department, Dexter moonlights as a serial killer, hunting and killing criminals who slip through the justice system. Dexter's sister, Debra, a vice squad officer, pulls Dexter into her world when another serial killer is killing prostitutes and leaving their bloodless bodies dismembered in various locations around Miami. Meanwhile, Dexter hunts a man who made snuff videos and killed a mother of two.

As Dexter stalks his next victim, a drunk driver who is about to be acquitted for vehicular homicide that resulted in the death of a teenage boy, the Ice Truck Killer strikes again and later gets in touch with Dexter. Meanwhile, when a cop is found murdered, Dexter helps Doakes and Debra investigate a crime boss who they believe is responsible.

"The Ice Truck Killer" strikes again and new homicide officer Debra is assigned the case, but she gets reprimanded for violating the chain of command; flashbacks offer insight into Dexter's homicidal tendencies and take him back to his first time "taking out the garbage"; Doakes gets on the bad side of a drug kingpin.

The Ice Truck Killer leaves severed body parts from his victims at locations that are linked to memories from Dexter's troubled childhood, which begins to get into Dexter's head.

The homicide division is handed an unbelievable lead when the Ice Truck Killer's latest victim is found alive but mutilated; Dexter is on the trail of a person who traffics in humans.

The Ice Truck Killer leaves a clue at the scene where Dexter has dispatched his latest victim, and Dexter is worried that someone might have witnessed his killing. Rita is trying to deal with her ex-husband.

The squad identifies the Ice Truck Killer; Rita's ex-husband, an abusive addict, is paroled.

Dexter appears to be connected to a psychiatrist suspected of murdering a suicidal patient.

While on a weekend getaway with Rita, his sister and her new beau, Dexter learns that his biological father, thought to be dead for 30 years, has just passed away, and that he's willed his son everything he owned.

The Ice Truck Killer prepares a crime scene for Dexter: a hotel room all covered in his previous victim's blood. But Dexter does not appreciate this gift, because his childhood memories hunt him.

The Ice Truck Killer sets a trap for Dexter by kidnapping someone close to him; Dexter's increasingly odd behavior piques Doakes's interest.

Dexter figures out who the Ice Truck Killer is, along with a dark secret from his troubled past. Meanwhile, La Guerta is replaced with a new boss and Angel figures out a way how to track the killer while he's still in hospital.

Things are really beginning to heat up for Dexter: Doakes' suspicions about him are growing, his victims are escaping, and his body dump site has been found. Meanwhile Paul is troubling Rita over the missing shoe and Debra is going through trauma over the Ice Truck killer incident.

Dexter is finding it hard to have closure on killing his brother. There is a new FBI agent to head the "Bay Harbor Butcher" case. Debra is finding it tough to put the past behind her.

Dexter sets his sights on a new victim: a murderer so repulsive it seems only fitting that he's a used-car salesman. Dexter's been unable to lie to Rita about his midnight activities, which has her thinking that he's a drug addict. She's threatened to leave him if he doesn't commit to a 12-step program to deal with his supposed addiction. While in this recovery, though, Dexter meets a sexy, mysterious woman named Lila.

Rita's estranged mother visits and senses something is wrong with Dexter. Masuka thinks he's developed a lead in the Bay Harbor Butcher case, which has Dexter concerned. Angel's interrogation of a witness crosses a line.

Dexter finds out that the man who killed his mother, right in front of him, is still alive. When he tells this to Lila, she suggests he face the man, as part of his road to addiction recovery. But then as his sponsor she insists on tagging along.

A copy-cat killer follows the lead of the "Bay Harbor Butcher." Dexter must destroy an incriminating surveillance video.

Dexter manages to get Doakes off his back. He devises a plan to get the police in another direction. Lila and Dex's relationship intensifies, and he has some interaction with Rita and the kids.

Dexter is attacked by the man who murdered his mother. Meanwhile, Lila wants to get closer to Dex, and Debra and Lundy close in on the Bay Harbor Butcher.

Dexter realizes it won't be easy to end things completely with Lila. Dexter tries to stay ahead of the investigations as the manhunt for the Bay Harbor Butcher intensifies. An enemy of Dexter figures out his secret.

Doakes follows Dexter to his next crime scene and shocks him with a revelation about Harry. The Bay Harbor Butcher task force feels they are zeroing in on their man.

Dexter must make a massive decision that will have an effect on all those he holds close. Lila meanwhile is back with a secret to blackmail Dexter.

Lila Tournay finds Sgt. James Doakes imprisoned in an Everglades cabin and learns from him that her object of affection, Dexter Morgan, is the serial killer known as the "Bay Harbor Butcher". She decides to help Dexter and kills Doakes by setting the cabin on fire. Meanwhile, Dexter's sister Debra questions whether her career is more important than her relationship with FBI Special Agent Frank Lundy.

After witnessing her brother kill Travis Marshall, Debra attempts to reconcile with Dexter 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.

Miami Metro sets out to unearth new evidence on a claim from a local convict that he has new information regarding a 15-year-old crime spree; Debra tries to cure Dexter of his killer tendencies.

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.

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.

Debra gets to know a local crime writer who's dug up some incriminating dirt on Hannah McKay (Dexter's newest obsession). Quinn gets an offer he tries to refuse and Batista is drawn to a new business opportunity. LaGuerta keeps digging into the Bay Harbor Butcher case.

Quinn falls back into his old ways as he makes some questionable choices to protect Nadia. Things heat up as Dexter and Hannah grow closer, but when Sal Price discovers the two are involved, he wants the exclusive story.

Fresh out of jail, Isaak renews his pursuit of Dexter while Quinn continues his power struggle with the Koshkas. Dexter tries to keep Debra in the dark about his relationship with Hannah, but a surprise visit from Astor, Cody and Harrison throws a wrench into his plans.

As Dexter scrambles to track down Isaak, a power struggle erupts among the Koshka Brotherhood, which could prove to Dexter's advantage. Meanwhile, Miami Dade tries to smoke out the Phantom Arsonist.

Dexter is unnerved when Hannah's father pays him a surprise visit; the Phantom Arsonist's crimes become more vicious; and Quinn defends Nadia's honor and finds himself in a volatile situation. Meanwhile; LaGuerta asks a former superior for help on the Bay Harbor Butcher case.

It's Christmas time, and Debra learns it may be better to receive when she gets a tip from Hannah's father... one that could lead to incriminating Dexter in a crime. Meanwhile, Dexter discovers that the man behind his mother's death has been released from prison.

Dexter must protect himself when LaGuerta closes in on his secret.