Batista puts Quinn up to Matthews for sergeant, and Matthews literally laughs in his face, so Batista takes it upon himself to help Quinn study for the test, but after getting frustrated with Quinn's thickheadedness, he unwittingly blows up his spot about leaving to bail Deb out in the middle of the night. When Jamie hears the truth, she's understandably pissed off and sad, so it's just as well she doesn't see what Quinn gets up to the rest of the episode.

To clarify what's referenced above, Deb gets arrested for drunk – like, wasted -- driving, and still not wanting to have contact with Dexter if she can help it, she calls Quinn to pick her up. Quinn succeeds in making the charges go away, but also tells Deb that when she turned him down, he hit the bottle much like she's doing now, and he's wondering what her reason for doing so is. She seems to want to tell him, but of course can't, so Quinn goes straight to Dexter with the news. When Dexter gives Vogel a quick summary of the fact Deb knows about him, Vogel is struck by Dexter's depth of feeling for his sister, and she later asks why, when she found out what he was, Dexter didn't kill her. Dexter tells her it's because he loves her, but Vogel points out that psychopaths see love differently than others, so he asks him to be specific, and when he obliges, she points out the things he claims to love are more about him than her. She also offers to try to help Deb, but Dexter refuses – initially.

MM finally tracks down Sussman's cabin – but when Dexter arrives, he and he alone knows that the crime scene has been altered, as Sussman is no longer hanging (from a hook stuck straight into his head, not from a noose as I originally thought). From the changes The Brain Surgeon (presumably) made, the evidence points to Sussman having killed himself, and this leads MM to close the case. However, Vogel gets a text from an unknown source telling her to look outside, whereupon she finds two "presents" on her doorstep – one for her and one for Dexter -- and unless the show is playing unforgivable shenanigans we can safely discount her as the killer. This time, The Brain Surgeon left her the occipital lobe, which is responsible for vision, and as such Dexter takes as a message that TBS is watching both of them. On the plus side, Dexter has been hard at work researching Vogel's "client" list, and he goes to check out one of the guys, who's currently selling fitness equipment at a mall. His investigation reveals that the guy isn't The Brain Surgeon – but he is a cannibal.

Elway gets TMI with Deb again about her sleeping-with habits, and on the one hand he seems reasonably nice and possibly normal. On the other, though, after getting a new case involving a cheating husband, Elway, sensing her hangover from across the room, gives Deb another "electrolyte" solution. Dexter then turns up all worried about the almost-DUI, and Deb reluctantly agrees to go to dinner with him, literally only so he'll go away and leave her and her headache in peace. At dinner, Dexter points out a man sitting happily with his family – who just so happens to be someone whose life Deb once saved in the line of duty – and tries to convince her that she's a good person. This only increases Deb's PTSD, though, and she drunkenly staggers into MM and tells Quinn she killed LaGuerta. Thinking she's just wasted, he drags her away from prying eyes, and although he obviously still doesn't believe her, he does suffer her to write down everything she remembers from that night while he goes to call Dexter.

In desperation, Dexter takes Vogel to the station with him, and on the way, she does point out that Deb accepting her punishment might be the best thing for both her and Dexter, but Dexter doesn't want to hear that, surely not least because Deb would have to bring him down with her. Dexter is forced to agree that Deb needs professional help at the very least, so with Quinn guarding the door, Dexter knocks a hysterical Deb out with an injection ("That was interesting!" Vogel HILARIOUSLY comments) as Vogel smoothly scoops Deb's confession while assuring Quinn that she'll treat Deb for her PTSD, and Quinn gets them out of there with no one else the wiser. Vogel assures Dexter that she can help Deb, so Dexter leaves his handcuffed sister in Vogel's care while he goes, I think, to dismember the cannibal? Hopefully that's as far as he takes the poetic justice.