Trama

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 finally believes he understands the beast Arthur Mitchell, known as the Trinity Killer. But when a ten-year-old boy goes missing, Dexter is forced to question everything he's learned up to this point. It's a race against the clock to find the boy before Trinity kills him, and with each step forward, Dexter has to confront the real possibility that he may have more in common with Trinity than he'd like to admit. Secrets abound: Cody defends one of Dexter's lies because he doesn't think Dexter would ever lie to him; Masuka, can't bring himself to confess what he witnessed at Thanksgiving; and Debra's recent discoveries force one of Miami's finest into making an impossible decision.

Open with Dexter and Rita taking Harrison to get his booster shots.

We see Dexter has moved all of his equipment to a shipping container. He reflects on it making sense, given his personal history.

Dexter stalks Trinity, with the plan being to grab him in the parking lot of his church. Trinity stops at a carnival where he follows a family of four. Dexter stays on his tail. Posing as a police officer, Trinity manages to get the family's son, Scott, to come with him to his van. Dexter sees this and screams out "Arthur" before Scott is hustled into the vehicle where his is chloroformed as Trinity gets away. Trinity calls Dexter (as "Kyle") and tells him that he has a process he needs to complete and if spots any police Scott will be killed. Trinity promises he will "preserve the boy's innocence." Harry wonders aloud whether taking a boy is a new part of Trinity's ritual.

Dexter goes to Trinity's house. Jonah tells him his father is on a trip for several days. Dexter/Kyle tells Jonah he needs to find his dad in order to keep him from doing something "really wrong" and has Jonah agree to search Trinity's office.

We see Trinity and Scott in a dark basement-looking room. Trinity is playing with a toy train and calling Scott "Arthur."

Dexter does some research and figures out that a 10-year old boy goes missing five days before every one of Trinity's cycles. There are actually four victims, the first representing Arthur himself. Lundy never figured this part out because the boys' bodies are never discovered.

At the office Dexter decides he needs to know more about the boy Trinity took. Dexter gives patrol Trinity's license plate for additional help. Outside Dexter's office Vince is trying to figure out how to tell Dexter about seeing Rita kiss Elliot. Debra cuts in front of him and demands that Dexter sit in on her Trinity briefing.

During the briefing they decide they will collect DNA samples from the school system. Angel has no leads on Lundy's shooting. Dexter blows Vince off when he tries to tell him about Rita. Christine shows up for the interview with Debra. Debra asks Angel to watch the interview on video because it could have something to do with the Lundy shooting.

Trinity wants Scott to put on a pair of pajamas. He tells Scott I'm "just trying to protect you, Arthur."

Dexter arrives at Scott's house and gets a few of the 'Missing' fliers. Through a conversation with Harry, Dexter figures out that Trinity's building sites would be convenient locations for holding a boy captive.

During the interview, Debra starts grilling Christine about how she was able to arrive at the shooting scene so quickly, given that she lives almost an hour away. She mumbles some story about getting up early to work out nearby, and Angel immediately sees that she's lying. Afterward Debra and Angel agree that there is something suspicious about Christine.

Dexter finds nothing at Trinity's current build site. Jonah calls and tells Dexter his father that a computer recent search history reveals that he had been searching real estate sites. He has Jonah send him the listings.

Rita breaks up a fight between Cody and another boy. The other boy said he saw Dexter leave the Young Sailors camp-out because he was scared. Cody was defending Dexter.

Christine calls Trinity. She says she needs to see her father sooner than her birthday, but he tells her he cannot.

Trinity returns to Scott with some food. Using it as bait, he convinces Scott to put on the pajamas.

Dexter begins trying listings looking for vacant houses. Rita calls him to tell him Harrison has a fever. At home, Rita tells Dexter she thinks the shots gave the baby a fever. She tells him about Cody's fight.

Angel and Debra discuss Christine. She mentions Christine is the same height as the shooter, but can't figure out why she would want to shoot Lundy. They decide to get Christine's DNA and check her priors.

Quinn is furious when Debra suggests his girlfriend might have anything to do with the shooting. Eventually he agrees to give her Christine's toothbrush. Debra has Vince run it.

Dexter continues checking real estate locations without any luck.

Quinn asks Christine about her family. She seems to suspect something is up. On her way out Christine leaves Trinity a message, saying they have to talk about "that woman in the bathtub that night."

Trinity begins weeping and tells Scott about his dead sister. He is able to convince Scott to have a bowl of ice cream, into which Trinity places some powder.

Dexter is informed that patrol spotted Trinity's van parked at a diner, which narrows his search to just a few houses in that area. Debra blows off Harry's old informant flame Valerie. Vince shows up and tells everybody that the DNA shows that Christine is related to Trinity.

Dexter finds the house where Trinity kept Scott, but sees they have already left the '60s-style bomb shelter in back.

Trinity meets with Christine in a parking garage. She tells him she knows about his murders, and shot Lundy and Debra to help protect her father. Christine thought she has covered it up well, but now thinks the police might be on to her. Trinity tells her not to worry, that he will stop by later. Once he is back in the van we see Trinity is pissed at this new development.

In the bomb shelter Dexter spots concrete residue. He and Harry realize that Trinity encases the boy victims in cement at his build sites.

Dexter rushed to the site and catches Trinity just before he is about to drop the still-alive Scott into concrete. Dexter and Trinity fight, with Dexter drilling him in the head with a shovel. Dexter is able to pull Scott out of the concrete and save him, but when he turns around Trinity is gone.

The doorbell rings at Christine's house. It is Angel, Quinn and Debra, there to bring her in for further questioning and likely arrest.

At home Dexter helps a crying Harrison go back to sleep. "I promise you no one's ever going to hurt you again,' he tells the baby. "Especially me."