Dexter manages his double life reasonably well for years, but his idyll is disturbed when he becomes involved in the investigation of a series of killings of prostitutes. The "Tamiami Slasher" has committed at least three murders already, as the novel opens. Dexter's sister, Deborah, wants out of Vice and into Homicide, and, knowing that her brother has eerie "hunches", asks him for help in solving the case.
Although Dexter admires the killer's style, he eventually decides to help Deborah due to "the Code of Harry". As the case progresses, he still feels a compelling pull to the killer due to similar wants—Dexter admits to himself readily that the bloodless and neat corpses appeal to him, as does the idea of cold and narrow spaces. After a lucid dream, Dexter drives around Miami late one night, when he spots a refrigerated truck and begins to follow it intently. A severed head is thrown at his car,indicating the killer knows Dexter was following him. The killer begins sending messages to Dexter, who finds the series of terrifying crimes engrossing and fascinating. Dexter is torn between helping Deborah catch the killer and a desire to sit back and admire the artistry and skill of a fellow monster's work, despite his earlier agreement to help his sister.
The killer kidnaps Deborah and brings Dexter to the scene, where he reveals that he is holding Deborah in the same shipping container his mother Laura was held in. The killer is Dexter's biological brother, Brian, who was separated from Dexter after their mother's murder at the hands of a drug dealer. Deborah's colleague, Migdia LaGuerta who is a spiteful, manipulative woman skilled only in political gamesmanship and doesn't care about other people; arrives and is killed by Brian, who is disappointed when Dexter refuses to kill Deborah. Dexter allows Brian to kill LaGuerta and helps him get away out of loyalty to his brother.