Dexter thinks Hannah didn't stop killing people, which makes her a perfect candidate for his victim, so he watches her, discussing with his dead power, how to proceed. According to the code, Dexter has to gather some solid evidence that would prove she poisoned her husband and her mentor. He wants to talk to her about this, but first he needs to regain her trust. He changes his blood report conclusion about the corpses that Hannah helped find, so that she wouldn't be a suspect, and shows a copy of that to her.
Quinn tells Nadia that her employers gave him a lot of money. She wisely tells him to return it, because he might end up being killed. Quinn agrees and throws money at George, saying "I'm not for sale", a statement, which is cocky as much as is untrue.
In a meanwhile, Isaak meets a representative of the hostile Colombian drug cartel in prison. Isaak breaks that guy's hand and mentions that negotiation is the key to success. He then talks to George and tells him to arrange the release as soon as possible, because the longer he stays in prison, the higher is the chance that he ends up killing somebody, in which case it will be very difficult for him to get out.
So George comes to meet Quinn instead of Nadia and demands that he does something to ensure Isaak is set free. If he doesn't Nadia will be transferred to a sex club in Dubai with unbearable working conditions. Quinn calls Nadia for a couple of days (as if she would pick up the phone in circumstances like that) and then eventually steals the evidence.
Sal Price, who's written a book about Wayne and Hannah, appears at Miami Metro to get the information about the newly found bodies. Dexter chases him and learns that Sal is writing a sequel solely about Hannah. So Dexter breaks into his apartment and steals the copy of the draft along with some other materials. He gets to know that Hanna's mentor was indeed poisoned with aconite, extracted from a plant.
Dexter comes to Hannah's place and finds the plant. She confronts him and asks why he keeps showing up, so he has to take her out... on a date.
Maria couldn't get anything from missing people's relatives, so she comes up with another idea: what if those suspects the police are looking for are not hiding, but are killed by Bay Harbor Butcher? For example that group of criminals, suspected in murders of girls, whose bodies were found in barrels (as we know, she's right about it, those men were killed by Dex and Lumen in season five). Debra tells Maria that it's unlikely, those criminals were really high profile,but she, of course, knows that Maria is right.
So Debra talks to Dexter and asks him about this case. She figures that the accomplice he had at the time was Lumen, and as usually, completely freaks out. Dexter tells her to relax and go on a date and she then kicks him out. However, she later takes his advise and goes on a date with Sal, where she learns that Hannah is very likely a killer and that Dexter's blood report was bullshit.
Dexter takes Hannah to the place she wanted to go with Wayne: Santa Holiday Adventure. As she watches fake snow fall down, Dexter injects her with his usual drug and prepares her for the kill. As she opens her eyes, he tells her his little secret, but in the end, instead of killing her, he cuts off the tape and has sex with her.
And yes, Batista wants to retire and run a restaurant.
So, Dexter seems to finally find a person that truly shares his interests. I think it's no coincidence that the story with Lumen came up: Dexter saw a soul mate in her, which turned out that she wasn't. Though Debra won't be happy if she finds out about it, she can't fully accept her brother for being what he is, she'll never put up with a girlfriend that poisons people.