The Ice Truck Killer leaves a clue at the scene where Dexter has dispatched his latest victim, and Dexter is worried that someone might have witnessed his killing. Rita is trying to deal with her ex-husband.

Dexter finds out that the man who killed his mother, right in front of him, is still alive. When he tells this to Lila, she suggests he face the man, as part of his road to addiction recovery. But then as his sponsor she insists on tagging along.

Dexter must make a massive decision that will have an effect on all those he holds close. Lila meanwhile is back with a secret to blackmail Dexter.

As Dexter struggles when Rita pushes to move in together before getting married, Miguel tells Dexter that a husband has murdered his two wives for a financial gain and gotten away with it. Dexter finds this to be the perfect candidate to get away and satisfy that dark urge which every man with relationship pressures go through. Dexter tracks the murderer to Bimini. While he is on the hunt, Rita disappears due to a medical emergency. Meanwhile, Debra works with Anton, her confidential informant to track down one of Freebo’s criminal confidants. But Oddly enough Debra finds herself attracted to Anton.

A series of chess-like moves ensues when Dexter and Miguel vie for the upper hand, with Miguel winning Rita's affection by presenting her with a lavish wedding gift. Elsewhere, Debra wonders if her relationship with Anton is worth the trouble.

Recent events spur Dexter into his own investigation of the Trinity killer. His motivations are now personal, and the clock is ticking. But the closer Dexter gets, the more he realizes that Trinity is unlike any monster he’s previously encountered. Meanwhile, Debra blames herself for events that were out of her control, and in so doing pushes away those closest to her. As LaGuerta and Batista close in on the Vacation Murderers, Batista realizes he can use Quinn’s relationship with a certain reporter to his advantage. And when Rita discovers a secret Dexter’s been keeping from her, she begins to realize just how little she knows about the man she married.

Dexter finally believes he understands the beast known as Trinity. But when a ten-year old boy goes missing, Dexter is forced to question everything he’s learned up to this point.

Dexter is saddled with an unwanted conspirator; Dexter worries about how Rita's death will affect Harrison; Deb works alone; Quinn enlists an old friend's help.

Dexter must do damage control; Debra's speculation begins to take shape; Quinn becomes involved in a homicide.

Brother Sam, a minister with a criminal history, is brought in by the homicide department to help solve a macabre murder, but Dexter sees him for what he really is, and it's definitely not a man of God. Elsewhere, Debra's sudden hero status elicits a pair of surprising proposals.

Dexter finds that in order to catch the Doomsday Killers, he must create a macabre tableau of his own; Debra's battle with LaGuerta over the case of the dead call girl boils over, and her therapist makes an unnerving suggestion.

Dexter tracks down another potential serial killer from Dr. Vogel’s list. Quinn celebrates his passing of the Sergeant’s exam by defending Debra’s honor in a fight. Dr. Vogel begins treating Debra for her PTSD.

Dexter is torn between fleeing the country with Hannah and Harrison, and taking Saxon out once and for all.