Dexter sleeplessly struggles to balance his new family life with his dark, murderous drive for a fresh victim, and his busier-than-ever forensic career pursuing a new target, "The Trinity Killer."
Dexter realizes that he has carelessly misplaced crucial evidence that could expose his dark side to the world, while helping to investigate new slayings that Agent Frank Lundy insists are the work of Trinity.
Dexter is hampered by his neighborhood's increased vigilance due to vandalism, his temporary inability to drive himself anywhere, and his admiration for the killing technique of the artful Trinity Killer.
Rita goes to a wedding with the kids, allowing Dexter to have his own little vacation. He does what he does best when alone, hunt, and goes after an officer with a dark secret.
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 doubles his efforts to stay ahead of the official Trinity investigation, and receives relationship advice about the friction between himself and Rita from a most unexpected source.
Dexter finally strikes a balance between family, career and his secret life, but is thwarted in his pursuit of his next victim, while Debra expresses a renewed and unwelcome interest in their father's checkered past. Miami Metro Homicide tries to solve the Model Killer Case.
Dexter wonders if his father's Code is truly the right path, and hopes to get answers by accompanying Trinity on an out-of-town road trip to Tampa; Debra discovers that her single-minded pursuit of Trinity has blinded her to the true identity of her assailant.
Dexter learns more about Arthur's bizarre and twisted world, while Rita has her hands full preparing Thanksgiving dinner for a full house, Debra uses the holiday to further investigate Trinity, and Batista gets closure on an old case.
The disappearance of a ten-year-old boy forces Dexter to question his assumptions about Trinity, while Cody defends one of Dexter's lies and Masuka is unable to face what he witnessed on Thanksgiving.
Dexter must buy time to protect himself when Debra's investigation brings the department one step away from identifying Arthur as the Trinity Killer; Rita confides in Dexter, but is disappointed in the result.
Dexter and Arthur find themselves on a collision course, as Debra unearths a shocking long-hidden truth, Rita admits her marriage to Dexter is troubled, and Batista and LaGuerta face the consequences of an ethics breach.
