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 Dexter a clue at the scene where Dexter has dispatched his latest victim and is worried that someone might of witness 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.

In the eighth episode (s1e8) the suicide of a powerful woman makes Dexter suspicious of her psychologist but he is in for a surprise when he meets the suspect because he appears to be aware of Dexter’s hidden side. Debra and Rudy’s romance is now warming up. Lt Laguerta also becomes skeptical of Neil Perry’s claim to be the Ice Truck Killer.

In the ninth episode (s1e9) Dexter comes to know that his biological father, Driscoll, who was said to have died 30 years ago, actually died recently ,leaving everything to him. Flashback shows Dexter questioning his adoptive father about his biological parents. Dexter suspects something odd in Driscoll’s death.

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.

In the eleventh episode (s1e11) another victim of the Ice Truck Killer, a prostitute with an artificial arm, is found. Dexter’s behavior arouses suspicions in Sgt. Doakes mind. Dexter traces a link between him and the Ice Truck Killer in a case involving his adoptive father, Harry Morgan and his biological mother. Meanwhile Rudy, proposes marriage to Homicide Officer Debra.

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.