There are numerous differences between the novel Darkly Dreaming Dexter and the Showtime series based on it; they range from extra subplots to rearrangements and modifications of elements from the source material.
The novel is narrated exclusively from Dexter's point of view and focuses mostly on his pursuit of the "Tamiami Butcher" (renamed the "Ice Truck Killer" for the series). With the exception of adoptive sister Deborah and adoptive father Harry, much of the supporting cast (Doakes, Angel and LaGuerta) have minor roles in the novel. The TV series expands on their characters with subplots not present in the original, such as Angel's rocky relationship with his ex-wife.
Another addition is the inclusion of Rita's abusive ex-husband. Although he is mentioned in the novel, he is never actually seen. In the show, he becomes a full-fledged supporting character who professes love for his children, but nevertheless still treats Rita violently.
The biggest change is the lead-up to and revelation of the identity of the Ice Truck Killer, called the Tamiami Killer in the book. In the novel, Dexter (and to a certain extent, the reader) is led to believe that Dexter himself might be the one committing the murders, due to a series of strange dreams that connect him to the murder; the possibility that Dexter's "Dark Passenger" is committing crimes when Dexter is asleep is brought up. The final clue is a blurry photo, taken from surveillance footage, of a man who resembles Dexter at a crime scene. After the Tamiami Killer kidnaps Deborah, Dexter (who is followed by Detective LaGuerta) finds and confronts him. It is subsequently revealed that the killer is actually Dexter's nearly identical long-lost brother, Brian, who, like Dexter, witnessed their mother's brutal murder. In the ensuing conflict LaGuerta is slain by Brian, Deborah finds out her brother is a killer and Dexter helps Brian to escape, an act referenced in the next novel.[6] As a morbid trophy, Dexter adds a drop of LaGuerta's blood to his collection.
In the television series, Brian is introduced under the fake name 'Rudy,' a prosthetist who becomes Deborah's boyfriend, and his relationship to Dexter only revealed late in the first season. Here, Dexter hesitantly kills Brian instead of letting him escape, Deborah does not discover her brother's secret and LaGuerta is not present at all in the confrontation. Furthermore, while in the novel Dexter and his brother are nearly identical, the actors playing the two characters are distinct from each other in their looks.
Some of the characters have had their names changed. Detective LaGuerta is named Migdia in the novel and Maria in the show while Doakes' first name is changed from Albert to James. Doakes' first name is not revealed in the first novel, but in the sequel Dearly Devoted Dexter.
The character of Angel Batista is a lab tech in the books while in the television series he is a homicide detective.
The character of Vince Masuoka is Eurasian in the books and appears even less socially aware than Dexter is.
The character of Camilla Figg is a young lab tech infatuated with Dexter while in the television series, she is an older woman who once worked with Dexter's father. She is the records supervisor and has a more maternal relationship with Dexter.