FLASHBACK: Mr. Wiggles' Playland in Florida. Dexter narrates how criminals fall through the cracks of the justice system, while we see the younger Dexter spy a clown, entertaining children. Dexter returns at night to search for clues. 

As he tells the story and mentions the Dark Passenger, Harrison interrupts, asking what that is. "Deb" urges Dexter to tread lightly.

Dexter explains his Dark Passenger to Harrison. Harrison asks why they are both like this, and Dexter explains that he also saw his mother murdered when he was young. Dexter tells Harrison about the Code.

Dexter describes the Code as we watch the younger Dexter go through Mr. Wiggles' things. He finds proof of Mr. Wiggles' crimes -- photos of murdered children. 

Harrison asks Dexter when Harry taught the Code to Dexter. Dexter explains he was around Harrison's age when he started exhibiting violent tendencies but that Harry never told the rest of their family. Dexter explains how he used the Dark Passenger for good.

At Mr. Wiggles' Playland, Dexter accosts the clown. Dexter explains that he kidnapped Mr. Wiggles and prepared a place to confront him. Dexter explains what he does to the "bad people" -- showing them their victims. As past-Dexter is about to stab Wiggles, "Deb" warns him that there is no going back if he tells Harrison about the murders.

Harrison asks if scaring and confronting those criminals made them stop. Dexter confirms that it did. Harrison takes it all in, overwhelmed. He asks if Kurt will come after them. Dexter suspects Kurt is long gone by now. Harrison goes to bed. Dexter sneaks out. He recovers Elric's body and completes his ritual of sawing up the body and disposing of it.

On Christmas morning, Angela continues to research the Bay Harbor Butcher. She notices a puncture wound on one of the Butcher's bodies and compares it to her photos of Jasper. Audrey appears, sees the new guitar under the tree, and hugs her mother.

Harrison wakes up and sees presents under the tree. Dexter has gotten him his own hunting rifle. Harrison asks if Dexter ever uses guns when he goes after the bad guys, but Dexter assures him that this is more about blending in. Harrison takes it outside, and under his father's guidance, shoots two bottles from a distance. Harrison asks if Kurt tried to kill him because Dexter was going after him. Dexter confirms this, telling Harrison that Kurt has been killing innocent women for the last 25 years. Harrison asks why Dexter hasn't told Angela, to which Dexter replies that he has no proof. Harrison suggests telling the police that Kurt attempted to murder him, but Dexter says the questions that could arise from that would put them in jeopardy.

Harrison presents Dexter with a gift of his own -- a sketch he has drawn of his Aunt Deb. Dexter is moved. He grabs one last gift for Harrison -- an ugly Christmas sweater.

In their sweaters, they visit Angela and Audrey to exchange gifts. Audrey serves up some monkey bread for Harrison and remarks that he seems different -- happier. Dexter remarks to Angela that they may have to navigate their kids becoming an item. Audrey brings out the monkey bread to Dexter and Angela. 

Harrison opens his present from Audrey -- an Iron Lake Hawks toque. Dexter opens his -- another ugly Christmas sweater. Harrison gives Audrey her gift -- a warm shawl. She kisses him on the cheek. Dexter gives Angela her present -- "The Police Handbook On Searches, Seizures, and Arrests." 

The doorbell rings. It's Kurt Caldwell, bringing a gift to show there are no hard feelings. Things get tense when Dexter and Harrison make their presence known. Kurt wishes them Merry Christmas and leaves. Harrison and Dexter quickly leave, saying they are going shooting. Audrey remarks to Angela how weird the encounter was.

Harrison expresses his concern about Kurt to Dexter. As they get in Dexter's truck, Harrison suggests doing to Kurt what Dexter did to Wiggles. Dexter says they'd need to find proof. He explains that serial killers often keep trophies or mementos of their kills. 

Angela visits Dr. Patel, the vet, asking about recent ketamine purchases. Dr. Patel finds four -- Mrs. Gross, Al Chung, Mr. Harris, and Jim Lindsay.

Dexter and Harrison fly the drone over Kurt's property. Harrison confesses that he planned the whole attack on Ethan so that he could get away with it. He asks Dexter how he knew, and Dexter explains that it was from his time as a blood-spatter analyst. Harrison apologizes for his previous behavior. He asks why Dexter never told him any of his history before now. Dexter replies that he needed to try out every other option first.

Harrison says he has been thinking about how simply scaring and hurting the criminals doesn't feel like justice. Dexter asks him what justice would feel like. Harrison talks about his fantasy of killing Trinity. On the drone control, Dexter notices something strange where Kurt disappeared. Harrison spies a vent. Harrison wants to go immediately, but Dexter tells him they should wait until dark.

Angela listens to the Merry Fucking Kill episode about the Bay Harbor Butcher. Dexter calls Angela to tell her that he and Harrison are going on a night hike to see the Blood Moon and won't be coming over. 

Kurt fixes and loads his rifle.

Dexter prepares his tools. "Deb" tries to talk him out of sharing the murdering with Harrison. Dexter insists that this is the only way to help his son.

Angela continues to take notes on Merry Fucking Kill. Audrey comes into the room, startling Angela. Angela asks Audrey about the Bay Harbor Butcher, wondering if they got the wrong man. Audrey says she's not sure, but she would have been scared to say so publicly as Molly did.

Angela calls Molly, but it goes straight to voicemail.

In his hunter get-up, Kurt hoses Dexter's home with propane and sets it on fire. He gets to a vantage point and points his rifle at the door, but no one comes out as the house goes up in flames. 

Dexter and Harrison arrive at Kurt's cabin. They search around the vent and woodpiles. Dexter finds a lock, which he picks and unlocks. It opens a metal door in the ground. Dexter tells Harrison to stay up and stand watch, but Harrison wants to come down. Dexter goes first. Harrison notices a surveillance camera. Dexter isn't worried. As Kurt watches the house burn, he gets a notification of his phone, seeing Harrison head down the tunnel. 

Dexter and Harrison find the embalming room, then head through to find where he keeps the preserved bodies of his victims in display cases. There are dozens, including Molly Park. Harrison asks Dexter if he killed Wiggles, which Dexter confirms. Dexter tells Harrison that he also killed Arthur Mitchell, the Trinity Killer. Harrison says Kurt needs to die. Dexter kisses him on the forehead.

Angela checks in at the tavern, asking about Molly. The hotel clerk tells her that Molly left a few days before Christmas. He takes her to the room in which Molly stayed. Angela asks to look in the safe. The clerk opens it to reveal Molly's camera and recording equipment.

Kurt returns to his home and packs up some money and essentials. Harrison surprises Kurt. Kurt reaches for his gun, and Dexter sticks Kurt with a needle, rendering him unconscious. 

Dexter sets up a kill room in Kurt's underground bunker/trophy room. Kurt is wrapped on the slab. Harrison asks about all the plastic. Dexter explains that they want to leave no trace. Harrison asks Dexter how many times he has done this, to which Dexter replies, "Hundreds." Harrison is stunned but realizes this means Dexter has saved thousands of innocent lives. Dexter tells Harrison that he can leave any time if it gets to be too much.

Dexter wakes Kurt. Kurt struggles, asking why they are doing this. Kurt admits it was him, explaining that he saved the runaways, protecting them from future trauma. Dexter calls him out, saying Kurt loved the power over his victims. Kurt remarks on Dexter and Harrison's bond, wishing Matt had been more like Harrison. Harrison asks why Kurt tried to kill him. Kurt explains that it was revenge -- "Jimbo" killed Matt. Dexter explains to Harrison that Matt fit the Code.

Dexter gags Kurt. He says Matt blamed Kurt, just as Kurt blamed his father. Dexter gives Harrison a chance to leave, but Harrison stays. Dexter stabs Kurt in the chest. 

As Dexter saws Kurt's limbs and packs them up, the blood seeps onto the plastic of the floor, oozing closer to Harrison. Harrison starts remembering his mother's death and decides to get out for some air after all. 

Finally, Dexter emerges with the full garbage bags. Harrison loads the bags into the RTV. They head to the incinerator and toss them in. Harrison asks what will happen when people notice Kurt is missing, but Dexter explains that Kurt already looked like he was going to run, which is what people will think happened. 

Harrison and Dexter arrive home, only to find their house burned to the ground. Audrey rushes to Harrison and hugs him. Angela questions Dexter, asking where he has been and why he hadn't answered his phone. He says they went on a hike and lost track of time. Audrey insists that Dexter and Harrison stay with them. 

Dexter goes to help the kids make breakfast. Angela opens a letter from her mailbox. In it is a note that reads "Jim Lindsay killed Matt Caldwell" and some titanium screws.