Season 1

Complete listed story — includes the ending

1. Dexter

Dexter Morgan ( Michael C. Hall ) is introduced as a serial killer who kills other killers who have escaped from, or haven't been found by the justice system. By day he is a blood spatter analyst who works for the Homicide Department of the Miami Metro Police. Dexter has a quasi-relationship with Rita Bennett ( Julie Benz ), a similarly troubled divorcee raising two young children while her former husband is in prison. One day, Dexter is called to a murder scene involving mutilated bodies, but with no blood visible. The murderer, soon to be nicknamed the "Ice Truck Killer", intrigues Dexter with this intricate methodology and a personal message in the form of a mutilated doll. At the same time, Dexter's hard-nosed sister Debra ( Jennifer Carpenter ), a vice squad officer, tries to gain a transfer into the Homicide Department.

2. Crocodile

Dexter assists detectives Angel Batista ( David Zayas ) and James Doakes ( Erik King ) in investigating the murder of an officer, who was working undercover investigating drug baron Carlos Guerrero ( Rudolf Martin ). Doakes is personally involved in the case, since he was having an affair with the officer's wife, who was also attacked. Meanwhile, Debra discovers the refrigerated truck in which the Ice Truck Killer dismembers his victims, and is promoted by her superior, Lieutenant María LaGuerta ( Lauren Vélez ), to the Homicide Department. Inside the truck, Debra, Batista, and Dexter find a block of ice with five fingertips in it, left deliberately by the Ice Truck Killer.

3. Popping Cherry

After the discovery of another victim of the Ice Truck Killer at an ice rink, the missing guard, Tony Tucci, becomes a potential suspect. Meanwhile, Rita receives an unpleasant visit from her ex-husband's drug dealer, who confiscates her car, forcing her to take the bus to and from her job as a hotel receptionist. Dexter selects his next murder victim while having flashbacks of his first killing—a nurse ( Denise Crosby ) who was caring for Dexter's sick father, Harry Morgan, but was administering overdoses of medication and slowly killing her patients. Elsewhere, Sergeant Doakes continues to harass Guerrero, as a group of renegade police officers decide to take matters involving Guerrero into their own hands.

4. Let's Give the Boy a Hand

As the hunt for Ice Truck Killer continues, posed body parts are discovered which appear to be the calling cards of an increasingly impatient killer. The Ice Truck Killer escalates his killing spree, leaving body parts of his latest victim at sites connected to Dexter's childhood, which leads Dexter to confront his dark personal history. As Halloween approaches, Rita kidnaps a barking dog from a cynical owner because it keeps her children up at night, and gives it to a loving family. Meanwhile, Lieutenant LaGuerta seeks to comfort the mother of the latest Ice Truck Killer victim. Dexter finds the victim mutilated but alive and strapped to a table for Dexter to kill. Instead, Dexter reports the crime scene anonymously to his sister. The pressure on Sergeant Doakes escalates when Guerrero's associates begin following him.

5. Love American Style

Rita learns that her colleague's fiancé, who was illegally immigrating from Cuba, is missing, and asks Dexter to investigate the problem using his police connections. He investigates Jorge Castillo, a salvage yard owner, and discovers that Castillo is murdering the smuggled immigrants who cannot pay for their freedom. Dexter discovers that Castillo's wife is involved in the murders, and kills both of them. Afterwards, he dumps their bodies in the ocean and frees their Cuban prisoners, not noticing a person watching him from the trunk of a car in the yard. Meanwhile, Debra and Doakes question Tucci about the Ice Truck Killer, and through him they find their first bit of tangible evidence.

6. Return to Sender

The body of one of Dexter's previous female victims has been found, despite Dexter's having thrown both of the corpses into the ocean. A young Cuban boy had witnessed the previous night's events, and Dexter dismisses his colleagues' leads that could direct them towards him. Eventually, Dexter frames the husband, whose body is still missing, with his wife's murder. The witness describes Jesus Christ rather than Dexter. During this time, Rita dissuades her abusive husband, Paul, from attending their daughter's birthday party after he is released early from prison.

7. Circle of Friends

Dexter must deal with Rita's menacing husband. Debra goes on a date with the prosthetics expert who made prosthetic legs for an Ice Truck Killer survivor. Debra and Angel are investigating the Ice Truck Killer and discover a familiar name with speeding violations near the scene of the Ice Truck Killer's third murder. Dexter investigates Sergeant Doakes's knife victim; he already knows the killer's identity but needs time to locate him. The Ice Truck Killer is finally apprehended, but Dexter doubts that they have caught the correct man.

8. Shrink Wrap

An unexplained suicide of a wealthy and powerful woman leads Dexter to suspect that her psychologist, Dr. Emmett Meridian, may have killed her. But he gets a shock when a visit to the suspect reveals dark secrets from Dexter's past. Elsewhere, Rita becomes warmer towards her ex-husband Paul, who claims to have reformed. She wants to become more intimate with Dexter, who is afraid of physically consummating their relationship, but then he is able to have sex with her and once they have finished, he is worried that he might have scared her. Meanwhile, Debra is falling in love with her new boyfriend Rudy. At the end of the episode, the audience finds out that Rudy is the Ice Truck Killer, while unknown to the characters.

9. Father Knows Best

Dexter learns that his biological father, Joe Driscoll, who he thought had been long dead, has only recently died and has left all of his belongings to Dexter, including his house. Dexter travels to the house with Rita. Debra and Rudy arrive there later (following Rudy's advice) to assist him in cleaning out the house. Dexter suspects Joe Driscoll's death to be murder. Flashbacks to Dexter's childhood show him questioning his foster father Harry ( James Remar ) about his real parents, and Dexter finds that Mr. Driscoll donated some of his blood to the young Dexter for surgery. In the last scene, one of Joe's neighbors, an elderly woman, recognizes Rudy as a cable repairman, who happened to be Joe's last visitor before his death; after Dexter, Rita, Debra and Rudy had left the premises, Rudy is shown returning to the elderly woman's house dressed as the cable repairman again. Meanwhile, Paul begins to slide back into his old abusive habits when Rita attempts to prevent him from seeing their children. Doakes is under investigation after shooting a fleeing suspect, and Batista wrestles with his conscience as he realises that the evidence doesn't fit Doakes's version of events.

10. Seeing Red

Dexter is sent to investigate a horrific blood-soaked crime scene, which he usually enjoys, but is taken aback by a long-suppressed memory of a childhood trauma instead. Rita is charged with assaulting Paul and could lose her children in a custody battle. However, when Dexter finds out, he decides to remove Paul from his and Rita's lives, but by framing him rather than killing him. Angel investigates a hunch regarding the Ice Truck Killer concerning amputee fetish; he turns to Rudy for help but ends up getting stabbed in the parking lot. Meanwhile, Rudy displays a growing interest in getting to know Dexter, particularly in the lately awoken trauma he had recently experienced.

11. Truth Be Told

The Ice Truck Killer strikes again, leaving a real nightmare before Christmas at Santa's Cottage. Sergeant Doakes becomes more suspicious about Dexter after his ambivalence about Batista's survival. Dexter finally finds he is connected to the Ice Truck Killer over a past case involving Harry Morgan and a blood-bath crime scene in 1973 involving Dexter's biological mother. Lieutenant LaGuerta braces herself as Captain Matthews blames her for the department's failure to find the Ice Truck Killer and he has her replaced. Rudy and Debra spend some quality time together, and Rudy proposes marriage to the smitten detective. Rita decides to take her children, Astor and Cody, to visit Paul, who has been sent back to prison.

12. Born Free

Doakes and LaGuerta begin to suspect that Rudy is the Ice Truck Killer, while Dexter finds a suspicious picture of the shipping container where his mother was killed. Doakes begins tailing Dexter, convinced that he is somehow connected to the Ice Truck Killer. A call from her ex-husband makes Rita suspicious of Dexter and his behavior. LaGuerta's replacement, Lt. Esme Pascal ( Judith Scott ) arrives and takes over the Ice Truck Killer investigation. Dexter recalls that Rudy is in fact his biological brother, whose real name is Brian Moser. Brian intends to kill Debra with Dexter in a reunion with his true family, but Dexter stops him. As the police close in, Brian escapes and Dexter is left with Debra, appearing to have saved her. The same night, Brian breaks into Dexter's apartment and attempts to stab Debra, but Dexter captures him. After an emotionally charged conversation, Dexter slices his brother's throat and leaves him upside down to drain, staging it as a suicide, while wondering what would happen if everyone knew the truth about him.