Previously: Lundy got killed and Debra got almost killed, and Dexter swore vengeance on Trinity, only he was a step too late and had to follow him home and was shocked to find the supposed lone wolf was a suburban family man. Just like Dexter's resentful for having to try to be!
Fittingly, as we see the title card reading "If I Had a Hammer," we hear Trinity singing an analogous religio-folksy tune in the middle of a church service. I would also very much like to believe that this image of John Lithgow standing at the front of a congregation would lead to one or more Footloose allusions, but in reality, the bulk of the irony at the moment is being used up on Trinity singing a song about being "washed in the blood of the lamb."
Anyway, Dexter stands among the congregation, singing along while his voice-over natters on about all the surveillance he's been doing on Trin (we see flashes of Trinity and fam doing their daily routines and learn he's a high school teacher). As always, Dexter's VO is half contempt and half admiration at Trinity's ability to blend into normal society so seamlessly.
Back home, evidence of Dexter's inability to do the same comes as we see Dex is moving all his stuff from his bachelor pad to the family homestead, apparently on Rita's orders. Not that it's made Rita one iota less furious at him. Dex can't seem to find a place for his metaphor -- err, lamp, not that Rita cares. She tells him there's food in the fridge if he's hungry, but when he says he could go for a sandwich, she turns and icily tells him they're out of bread. DVO thinks she has to forgive him eventually...right? She tells him she's made an "emergency" appointment with a new therapist, because of course these marital problems are urgent, or doesn't Dexter think so? Honestly, it's one thing that Rita's being written as a raging bitch this season -- it's not subtle and fairly inelegant but I see where the writers feel it's necessary. But honestly? It's the passive-aggressiveness, combined with those easy jabs at therapy-culture, that really make me hate her. They do know they've written Rita past the point of no return for most fans, right?
Anyway, later on, Deb asks Dexter for a ride in to the station (looks like she's still staying in Astor's room) -- they're interrogating Nikki Wald again. She's confessed to everything but shooting her and Lundy. While DVO plays to the Helen Keller crowd (reminding us that's because Trinity shot her and Lundy, though Dexter doesn't want her to know that), Dexter gets a call about a bludgeoning downtown. Debra correctly guesses the address and knows it's the third Trinity victim. Deb's expression is half pride that she and Lundy had the right spot and half raging regret that they were both gunned down before they could stop it. Dexter tells her it's going to be okay. DVO: "Because I'm going to kill him for you." No, really. That's what it's come to. The show isn't quite sure we all realize that Dexter kills people, pretty much constantly, so they need to throw in that extra crutch just so we don't forget and start wondering when he's going to start selling weed or transition into the housewife personality. DVO, you're on probation until you can find something useful to say.