The second installment in Jeff Lindsay's Dexter series finds its protagonist, Dexter Morgan, a serial killer who works as a blood-spatter analyst for the Miami-Dade Police Department, unable to indulge his compulsion to kill. Dexter is guided by what he calls the "Dark Passenger," an internal presence that drives him to murder, and by a code instilled by his late foster father, Harry, a former cop: Dexter may kill only those who are guilty of murder and who have escaped justice. Sergeant Doakes, a fellow officer and decorated army veteran who has long suspected Dexter, now believes him involved in the recent death of Detective LaGuerta and has escalated to active surveillance, trailing him everywhere.
Before Doakes began watching, Dexter identified a target: Randy MacGregor, a real estate agent who preyed on young boys. Dexter traced MacGregor to two missing children, searched his cabin cruiser, found evidence of murder, and killed him. Photos on the boat revealed an accomplice whose red cowboy boot appeared in several shots, but MacGregor died without naming the photographer. Returning to the boat, Dexter found a note leading to Steve Reiker, a children's photographer in Coconut Grove. Driving home, Doakes pulls alongside and announces, "I'm watching YOU" (29). With Doakes shadowing him, Dexter cannot pursue Reiker. He adopts a strategy of relentless normalcy, spending evenings at his girlfriend Rita's house with her children, Cody (age six) and Astor (age nine), hoping to bore Doakes into giving up.
Three weeks later, Dexter and his sister Deborah Morgan, recently promoted to sergeant in homicide, are called to a crime scene near the Orange Bowl, a football stadium in Miami. Inside a small house they find a living human being surgically reduced to a limbless, tongueless torso, strapped to a table in front of a mirror. The victim's eyelids have been removed, forcing him to watch his own reflection. Every wound is professionally cauterized, and drugs keep him conscious. A note reads "LOYALTY." Doakes's reaction is not horror but recognition, and he immediately contacts Captain Matthews.
Matthews introduces Kyle Chutsky, a large, scarred man from Washington who orders the department to stand down. Chutsky selects Deborah as his liaison, and the two quickly become romantically involved. Dexter deduces that Doakes recognized the crime from his military past: Before joining the police, Doakes served in Army Special Forces with a period of "detached service" in El Salvador, a country then engulfed in US-backed covert operations involving torture and political killings. The torturer, nicknamed Dr. Danco, discovered he could inflict suffering without empathy and volunteered for covert Special Forces, where his talent for surgical dismemberment flourished. Doakes served as a "shooter" on the same team. When political winds shifted, the US government betrayed Danco, handing him to the Cuban-backed opposition, who imprisoned him. After years of captivity, Danco was turned by his captors. Now free, he possesses a list of the men who betrayed him, and Chutsky admits both his and Doakes's names may be on it.
Deborah calls Dexter in the middle of the night: Chutsky has been taken. The next morning, a courier delivers a box containing a human finger wearing Chutsky's diamond pinkie ring. Dexter moves Deborah to his apartment for safety. They pursue the few leads available: The first victim is identified as Manuel Borges, and a neighbor describes the suspect as small and bespectacled, driving a white van with a Florida CHOOSE LIFE specialty plate. Washington's replacement agent, Dan Burdett, is also captured and killed, his dismembered body found with a note reading "POGUE," military slang for a desk-bound bureaucrat. With no outside help coming, Dexter proposes recruiting Doakes. Matthews assigns him to the case. Doakes agrees but warns Dexter: "When this is over. Just you and me" (157).
Meanwhile, Dexter's personal life takes an unexpected turn. On a fishing trip, Cody catches a fish and, when Dexter looks away, stabs it repeatedly with a fillet knife, smiling at the blood. Later, Chutsky's pinkie ring, which Dexter has been carrying since removing it from the severed finger, falls from his pocket at Rita's house. Rita discovers it and assumes it is an engagement ring, appearing at the door weeping with joy. Unable to correct the misunderstanding, Dexter finds himself suddenly engaged.
Doakes and Dexter devise a plan to use the engagement party, hosted by colleague Vince Masuoka, as a trap. Doakes gives Dexter a GPS tracking system as insurance, and they broadcast scripted messages on police frequencies advertising Doakes's location. Earlier that day, Doakes approaches Oscar Acosta, a former team member living in Miami, who panics and flees. A chase follows, during which Danco's white van rams Deborah's car into a retention pond. Submerged and dazed, Dexter thinks of Cody and realizes the boy carries his own Dark Passenger, born from the same kind of traumatic childhood Dexter experienced. This realization spurs him to escape and rescue Deborah, who is unconscious with a broken collarbone. They find another dismembered victim in the crashed van but lose both Oscar and Danco.
That evening, Dexter confirms his suspicion about Cody. Astor reveals that Cody killed a neighbor's dog and enjoys hurting things. Dexter tells the children he understands and tells Cody, "We have to get you squared away" (213), echoing Harry's words. At the party, while Dexter is trapped inside amid raucous festivities, Danco takes Doakes. Using the GPS system, Dexter tracks the signal to a gator farm deep in the Everglades. Inside, he finds Chutsky alive but missing his left arm below the elbow and right leg below the knee. Danco has fled with Doakes.
Dexter delivers Chutsky to his hotel and brings Deborah to him. She takes his only hand in her only hand and tells him to sleep. Chutsky provides a list of the El Salvador team members still in Miami. Dexter deduces that Danco, having lost his safe houses, will have moved into his next victim's home. He drives to the house of Wendell Ingraham on Miami Beach and finds Danco inside, with Doakes strapped to the table, both hands gone at the wrist. Danco spots Dexter's reflection in a mirror and tranquilizes him with a dart gun. Dexter wakes bound on the floor and pieces together Danco's pattern: The doctor plays hangman with each victim, assigning a word representing a virtue they supposedly violated. Wrong guesses cost body parts, and the notes found at each scene are the completed or partially completed words.
Chutsky and Deborah arrive. Chutsky fills the doorway with a gun, but Danco tranquilizes him. As Chutsky collapses, Deborah, standing directly behind him, fires two shots into Danco's chest, killing him. She frees Dexter and kneels beside Doakes. The note on his table reads "TREACHERY," with five of nine letters crossed out, meaning Doakes lost five body parts. Doakes stares at Dexter with wordless hatred, but Dexter reflects that the sergeant will never follow him again.
In the epilogue, Dexter is at sea aboard MacGregor's cabin cruiser, having completed his long-delayed kill of Reiker. He sinks the body into the Gulf Stream and scuttles the boat, destroying all evidence. Dexter contemplates his future: He will marry Rita for permanent domestic cover and guide Cody along the "Harry Path," teaching the boy discipline and control the way Harry taught him. As the sun rises, Dexter turns his boat toward home.