He's smart, good-looking, and he's got a great sense of humor. Michael C. Hall stars as Dexter, everyone's favorite serial killer. He spends his sun-drenched days solving crimes - and moonlit nights committing them. But not to worry, our cool-blooded Dexter doesn't kill just anyone. He reserves his homicidal hobbies to talking only the lives of other killers. Some might say he's crazy, but others say he's making the world a better place.
Dexter Morgan, Miami Metro Police Department blood spatter analyst, has a double life. When he's not helping the Homicide division solve murders, he spends his time hunting and killing bad guys who slip through the justice system. His sister, Debra, a vice squad officer, pulls Dexter into her world when a series of hookers are being murdered around Miami. With his help, she sees a chance to get on the good side of Lt. LaGuerta, thereby strengthening her request to transfer to Homicide. Meanwhile, Dexter's girlfriend, Rita Bennett, a single mother of two whose abusive ex-husband is in jail, suddenly wants to take their relationship to the next level. Dexter has to cope with her more-urgent physical demands on him at the same time the killer leaves him a cryptic invitation to "play."
Dexter is stalking his next victim, a drunk driver about to be acquitted for the murder of a teenage boy. But when a fellow cop is found murdered, Dexter has to put that on hold to help Homicide Detectives Batista and Doakes investigate a crime boss suspected of the murder. It gets even more personal when the crime boss also orders a hit on the wife of the murdered cop. Meanwhile, the hooker-hunting Ice Truck Killer strikes again and leaves a macabre piece of evidence that Debra finds, gaining her the transfer she wanted out of Vice and into Homicide.
Dexter is called in to help Debra with the investigation into the Ice Truck Killer's latest murder, while Dexter hunts his latest victim, a teenager named Jeremy who is a recently released murderer who looks like he's about to kill again. Despite Debra and Dexter's protestations, Lt. LaGuerta starts a manhunt for Tony Tucci, the nightwatchman videotaped at the ice rink where body parts were found. But while the manhunt for Tucci begins, a skeptical Debra keeps looking for the "real" Ice Truck Killer. Meanwhile, Doakes decides to go after the crime boss at his church, confronting him and his daughter about his part in the murder of a cop and his wife. Rita, Dexter's girlfriend, has her own troubles when someone from her incarcerated husband's past comes to visit, demanding repayment of drugs lost by her husband.
Dexter's past comes to life when body parts begin appearing throughout Miami, gifts from the Ice Truck Killer. The horrific tableaus created in places of Dexter's childhood memories start to make Dexter question his own past and his reasons for controlling his dark urges. Meanwhile, LaGuerta's hunt for Tony Tucci has to go in a different direction when new information comes to light about Tucci and his connection to the Ice Truck Killer. Doakes, the lead investigator of the Ice Truck Killer case, becomes afraid for his life when a crime boss puts his thugs on the trail of Doakes, 'innocently' following him wherever he goes.
Debra's discovery of an Ice Truck Killer victim being found alive gives LaGuerta and her Homicide detectives their first chance to identify the notorious serial killer. Debra and Doakes, assigned to the case, sit with the mutilated victim, in the hopes that he will be able to identify the killer. While Dexter works on the case, Rita tells Dexter about a friend of hers whose fiance has disappeared while immigrating from Cuba by way of a coyote (a human trafficker). When the fiance turns up dead, Dexter decides to hunt down the murderous coyote. But things don't go as planned when Dexter realizes that there is more to the vicious trafficker than his careful stalking prepared him for.
Dexter arrives at a crime scene to find one of his victims he has disposed of has mysteriously returned to the scene of the kill. Dexter figures that it's the Ice Truck Killer, letting him know that he knows what Dexter is up to. The noose is tightened further, when LaGuerta finds a young Cuban boy hiding at the crime scene — there's no way he missed seeing Dexter capture the victim. Dexter has to figure out a plan to stay out of the crosshairs of his own Homicide Division while investigating his own crime. Meanwhile, Rita has to deal with her abusive ex-husband, Paul, when he's released from jail and wants to come to their daughter's birthday party.
Debra and Batista find proof that Neil Perry is the Ice Truck Killer when they find a body beneath Neil's trailer home. A manhunt ensues to find and capture Neil before he kills again. As more and more evidence rises to the surface, Dexter is left adrift. Neil Perry, the supposed Ice Truck Killer, doesn't live up to his expectations. Meanwhile, Dexter has to deal with his past when a teenager he caught and released murders again. As a result, Dexter sets out to correct this mistake in one of the only ways he knows how. Rita's family life is torn asunder as her paroled ex-husband, Paul, reasserts himself as the father of her children. Paul even confronts Dexter, letting him know that he doesn't like Dexter being around his wife and kids. Rita wishes that Paul would go away forever, something that is definitely possible when your boyfriend happens to be Dexter.
While looking into a series of suicides of high profile, powerful women, Dexter realizes a pattern: they all saw the same shrink. Dexter goes into stalk mode and becomes a patient of the shrink to ascertain whether or not he is the killer that he seems to be. Unexpectedly, the shrink helps Dexter unlock dark secrets from his past. Debra's latest relationship with Rudy also quickly heats up. Dexter's relationship with Rita, however, seems to be in danger as Paul works his way deeper into Rita's life and much to Rita's consternation, the kids love him and he's actually civil to her. Meanwhile, Dexter's certainty that Neil Perry is not the Ice Truck Killer helps LaGuerta to decide to not just accept Neil's confession, despite mounting evidence to the contrary.
Dexter receives a registered letter that informs him that his biological father has recently died. This comes as a shock, because Harry, Dexter's adoptive father, had told Dexter that his real father had died over 30 years ago. As Dexter takes off to reconnect to his shadowy past, Rita decides to come along to help him make it through the weekend. Then Debra and Rudy join them for the weekend at the dead bio-dad's house and things become even more awkward. Back in Miami, Doakes is involved in the questionable shooting of a middle-aged Haitian man. Internal Affairs investigates and Batista has to decide if he's going to tell the truth about the shooting, or back Doakes' untrue version of the actual incident.
Dexter's world is shaken when he is called to the crime scene of a massacre unlike any that he's ever seen before... or so he thinks, until a series of memories comes streaming back that shock him to his core. Meanwhile, Rita has to hire a lawyer when Paul brings a surprising case against her to take sole custody of their children. Batista follows a new lead on the Ice Truck Killer case that brings him one step closer to apprehending the sadistic serial killer. But does it bring him too close?
The Ice Truck Killer strikes again, leaving a real nightmare before Christmas at Santa's Cottage. But this time, Dexter notices that the kill is not as 'tidy' as the previous kills, as if the Ice Truck Killer is rushing to leave Miami. But in reality, the Ice Truck Killer has kidnapped someone very close to Dexter to lure him into a trap that will change Dexter's life forever. Meanwhile, Sgt. Doakes notices that Dexter has been acting strangely around the Homicide division, making him wonder if in fact, Dexter is the Ice Truck Killer.
Dexter's loyalties are put to the test as he follows clues that the Ice Truck Killer leaves for him. But as Dexter goes on the hunt, he wonders just how deep he will have to go down the Ice Truck Killer's dark and demented path. Doakes, still thinking that Dexter may be the Ice Truck Killer, uses questionable methods to stop Dexter from his hunt for the Ice Truck Killer. Meanwhile, as Dexter remains unavailable to Rita, her ex-husband, Paul, tries to convince her that Dexter is a very dangerous man to have around their children.