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.

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

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 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.