The book contains elements of cannibalism. Lindsay said of the research he put into writing the novel, "There are cannibal chat groups...just dying to give you a recipe for how to prepare and cook human flesh."
Nine months after the previous book, Dexter and Rita's daughter Lily is born. The birth brings remarkable changes in Dexter; apart from feeling genuine love and emotions for the first time, he also does not feel his "Dark Passenger's" compulsion to kill and vows to swear off his dark hobby in order to be a good father for his daughter. Dexter is called to a crime scene by his sister Deborah, who is in the middle of a jurisdictional fight with the FBI over a reported kidnapping. Dexter believes that the large quantity of blood found there was planted, and that the missing girl in question, Samanatha Aldovar, is faking her disappearance in order to get money from her parents. Dexter runs tests and discovers that the blood type does not match Samantha.
Deb and Dexter go to Samantha's private school and talk to her principal, who is initially reluctant to divulge any information. This changes when the principal discovers that Samantha's friend Tyler Spanos, a wild child, is also missing. Subsequent interviews with their friends indicate that they were both befriended by a young man with teeth filed down like fangs, and that only a few dentists in Miami offered such a service. Their prime suspect is Bobby Acosta, the son of a wealthy city official who already rescued Bobby from felony prosecutions.
Dexter is surprised when his brother Brian, whom Dexter last saw several years previously, brings Astor and Cody home from school. Brian quickly ingratiates himself with Dexter's family, who rapidly start to adore him - much to Dexter's dismay. Dexter soon receives another call from Deborah and arrives at a crime scene where someone was apparently cooked and eaten. DNA from the gnawed bones matches that of Tyler Spanos. One of the detectives working under Deb uses his contacts and arrests two Haitian men, who swear that they saw Bobby leaving Tyler's car at a chop shop.
Deborah and Dexter arrest Victor Chapin, another young man with artificial fangs, but are forced to release him when a public defender shows up. Dexter, in a fit of overprotective fury over his daughter, stalks and kills Chapin. Just before dying, Chapin admits to having taken part in eating Tyler. Things get worse when the remains of Deke, Deborah's obnoxious partner, are found partially eaten. Rummaging through a nearby trash bin, Dexter finds Deke's blood-sodden shirt and a souvenir chip from a local goth nightclub called Fang. The duo force their way into the club and find Bobby, but are thrown out by the club's manager. They wait until the club closes, after which Dexter breaks in to search for Samantha.
Dexter remembers that he had previously considered the club manager as a victim, after a large number of migrants vanished after working at Fang. Dexter eventually finds Samantha in a large refrigerator. However, rather than follow Dexter to freedom, Samantha locks them both inside. Samantha reveals that she desires to be eaten, and that she and Tyler volunteered to let the cannibals cook and eat them. The two are then taken to a trailer in the Everglades, where they are left with only a jug of water. After drinking MDMA-laced water, Dexter and Samantha become euphoric and have sex multiple times. Shortly afterward, Deborah and the Miami PD arrive and arrest the cannibals, but end up killing the club manager. Samantha, irate at being rescued, threatens to falsely accuse Dexter of rape as revenge for ruining her fantasy.
The next day, Deborah tells Dexter that Samantha has run off again. They approach Bobby's father Joe, who refuses to turn his son in. However, Bobby's stepmother Alana privately divulges that Bobby is at an abandoned amusement park that his father owns. There, Dexter, Deborah and Chutsky are captured by a cannibal "coven", which turns out to be lead by Alana. Deborah and Chutsky are taken away, leaving Dexter to watch Alana grill a slice of a semi-conscious Samantha. As Alana prepares to carve Dexter, his brother Brian — disguised as one of her guards — shoots her and other members of the coven. Brian cuts Dexter loose and reluctantly helps him rescue Deborah and Chutsky. Whilst fleeing they check on Samantha, who is dying of her wounds; Dexter assures her that her flesh was "delicious," allowing her to die content.