After an afternoon at Habitat for Inhumanity, the van drops everybody off in front of Arthur's house. Dexter follows him back to his garage. He brandishes a box-cutter, like we really think he's gonna off Tinity in episode six. Instead, he uses it to cut his own hand, the better to use as a pretext to getting inside Arthur's house. Arthur goes to get the first aid kit and instructs Dexter to make himself at home. Dex scopes the place out, the wall of family photos, the washer/dryer unit, the lamp (DVO grumbles that Arthur has a place to put his lamp). Then Dexter comes upon it: a wall adorned with plaques from each of his Habitat for Inhumanity builds. Each one corresponding to a city and year that the Trinity killings took place in. It's a bingo! DVO connects the thematic dots for us: These are Arthur's equivalents to blood slides, and he's keeping them not locked up in a secret apartment, but out in the open. DVO's been much more effective this week when it's been sarcastic and bitchy, so I just wish he'd bust loose with a "Jealous!" and get things over with.
So now that he's seen Trinity's trophies, I guess Dexter figures it's time to rattle the man's cage (shades of Officer Zoe the Family-Killer). He spots a flowery urn on the table in front of the plaques, the nameplate revealing that the ashes belong to Arthur's sister. DVO notes, humorously, that the ash supply has gotten low after 30 years of being left, bit by bit, at crime scenes. Arthur calls for "Kyle" from another room, and instead of scrambling to look innocent, Dexter instead picks up the uncovered urn and turns to anticipate Arthur. He wants to see what happens to Arthur when his "weak spot" is exposed. Arthur rounds the corner and freezes when he sees Dexter with the urn. He walks right up to Dexter, carefully takes the urn and puts it back on the table...and then SLAMS Dexter up against the wall, his forearm on Dex's throat. "Don't! Touch! My sister!" he wails, clearly dipping back into unhinged territory. Dexter struggles to breathe, and after a moment, Arthur releases him and apologizes.