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 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.

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.

Miami Metro is just one step away from discovering the identity of the Trinity Killer. And Dexter can't let that happen. Dexter must take drastic action to buy himself time to deal with Trinity in his own fashion. Arthur, who still can't understand why Dexter didn't simply turn him in, begins his own bloody investigation into Kyle Butler.