The police close in on the Trinity Killer, who cautions Dexter to keep away. But Dexter is willing to do whatever he can to get his man, legal or not. Meanwhile, LaGuerta and Batista must answer for their breach of ethics; and Debra becomes privy to something she’s not sure she wanted to know.

Dexter needs to buy some time to protect himself when Debra’s investigation brings the department away from identifying Arthur as the Trinity Killer.

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

It is Thanksgiving and Dexter continues to get closer to Trinity. Rita prepares Thanksgiving dinner and Debra continues to investigate the Trinity Killer.

Dexter wonders if his father’s Code is the right course and hopes to get answers while on a road trip with Trinity. Meanwhile, Debra discovers that her single-minded pursuit of Trinity has kept her from knowing the truth.

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 Miami Metro discovers the Trinity Killer’s latest handiwork. Therefore, he has to work doubly hard to stay one step ahead of their investigation. Meanwhile, Debra becomes frustrated when she finds herself shut out from her own case. She considers bending the rules in the name of justice, risking her career in the process. LaGuerta and Batista come to regret a major decision, and realize that by playing by the rules they may have painted themselves into a corner. And when the friction between Rita and Dexter comes to a head, Dexter gleans relationship advice from a most unlikely source.

Dexter is inspired to investigate the Trinity Killer on his own, while Debra blames herself for an event that was out of her control, and Rita realizes how little she knows her husband after discovering one of his secrets.

Dexter gets some much-needed R&R time with Rita and the kids out of town, leading to his stalking of a new victim – until he unexpectedly begins to empathize with his target, a cop that murdered her family.

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.