The final challenge between Dexter and Arthur comes. Debra finds out a long hidden truth. Rita admits that her marriage is troubled. Batista’s and LaGuerta’s relationship must face consequences.

Dexter must stop Debra’s investigation from identifying Arthur as the Trinity Killer. Meanwhile, Arthur himself is trying to identify the whereabouts of Dexter’s alter ego Kyle Butler.

Dexter thinks he knows the ins and outs of the Trinity Killer until a 10-year-old boy goes missing.

Dexter continues to try to understand The Trinity Killer by talking to his family; he discovers that Arthur Mitchell may not have the perfect mask after all. With Dexter out on the prowl Rita gets a little help with her busy household from her handsome next door neighbor, but his motives may not be all that honorable. Debra continues to investigate the Trinity Killer and may be getting a little too close for her own safety.

Dexter goes on a house-building excursion with Trinity, but still doesn’t kill him. The team investigates more into the Trinity case and Rita gets close with a neighbor while Dexter’s out of town.

Dexter seems to have finally managed to balance work, family, and his dark passenger. But he knows the balancing act can’t last. A series of murders leads the department to a prominent photographer, prompting Dexter to move him to the top of his list which doesn’t sit well with Harry. But Quinn’s effort to bond with Dexter poses a problem with hunting the new prey. Meanwhile, Debra returns to work and focuses on finding the Trinity Killer, which Dexter fears will put her in danger.

Dexter knows it’s only a matter of time before the Trinity Killer’s latest handiwork is discovered by Miami Metro. He has to work doubly hard to stay one step ahead of their investigation. Debra is shut out from her own case. She considers risking her career and bending the rules in the name of justice. LaGuerta and Batista realize that by playing by the rules they may have painted themselves into a corner. Dexter gleans relationship advice from a most unlikely source when the friction between Rita and Dexter comes to a head.

Debra recovers from the shooting but is emotionally distraught from Lundy’s death and other life events. Dexter realizes that it was the Trinity Killer and not the Vacation murderer as the rest of the police force thinks. He gets closer to the Trinity Killer than he has before.

Dexter is left home alone and with free time as Rita takes the kids on a vacation which may prove interesting for Dexter in several ways. In the meantime two other relationships are on the line: LaGuerta and Batista debate about their future and Debra’s own, as she helps Lundy with the Trinity Killer investigation.

When a rash of vandalism strikes Dexter’s new neighborhood, the increased vigilance of his neighbors impacts his ability to take care of his side business, and it doesn’t help matters that he is temporarily unable to drive. As for the Trinity Killer, Dexter is developing an appreciation and admiration for his incredibly impressive technique.