Deb and Dexter have some honest, open and very disturbing communication in “Sunshine and Frosty Swirl.”

So Deb knows. She knows her brother, her co-worker, her friend, her (ridiculous) crush, is a serial killer and has been for a long time. “Sunshine and Frosty Swirl” opens with Deb running away from Dexter’s apartment.

Dexter pursues her and when she stops to vomit on the street, he narrates: “I’ve dreaded this moment my whole life. But I never pictured it like this.” He attempts to comfort her, in his dulled emotional state.

She tells him: “I am not okay. I am never gonna f—ing be okay.” Amid an expectedly inventive panoply of f-bombs from Deb, Dexter reveals he’s been killing since he was 20, that he only kills certain kinds of people as per Harry’s code, that he calls his mania his Dark Passenger (“You gave it a name?”).

Inside again, they debate the definition of “victim,” with Deb pointing to the slides and Dexter pointing to himself. Justifying himself, Dexter tells her, “Sometimes the system doesn’t work. Killers fall through the cracks.” It’s like the series premiere, in which Dexter had to convince the audience to keep watching. “Don’t I f—ing know it,” Deb retaliates, “I’m talking to one right now.”

Throughout the episode, Dex and Deb get nearly everything on the table (no pun intended) and Dexter has some much-needed soul searching with his mind’s image of his father, Harry. Deb feels inexorably torn — she’s a lieutenant and now an accomplice in the season opener’s faux tableau. The next day, she tells Dexter her plan: he’ll move in with her and she’ll watch him constantly. He has no choice in the matter.

“I still believe that there is good in you,” Deb tells him outside the station. Too bad Dexter doesn’t.

Meanwhile, Capt. Maria LaGuerta finds last week’s slide to contain Travis Marshall’s blood and sentimentally looks at a picture of Sgt. James Doakes. What’s she going to do with this knowledge?

Sgt. Angel Batista and Joey Quinn make inroads at the Ukrainian mob-associated strip club, which is run by this season’s apparent primary villain, a menacing Isaak Sirko. We later see Sirko murder a club informant who had helped Miami Metro.

Dexter struggles with his need to kill, especially when faced with the annoyance and threat of intern Louis Greene. After the fracas of Deb’s rummaging, Dexter finds a model hand from the Ice Truck Killer on his table. Vince Masuka tells him the hand was bought by an online bidder. Dexter connects the dots, goes to Greene’s apartment and intimidates him. Louis tells him the tormenting is his revenge for Dexter’s harsh words about his serial killer video game last season. Yeah, okay.

Dexter tells him he never wants to see him again, but a few scenes later, there Louis is in Dexter’s apartment, flaunting his presence as babysitter Jamie’s boyfriend. Dexter, don’t kill him!

He almost does. Sneaking out of Deb’s apartment, where he’s now under house arrest, after some incisive and insightful conversations, Dexter shoots Louis up with M99 and throws him in his trunk.

But then he calls Deb and tells her he’s about to kill. They had talked previously about Dexter’s emotions when he gets the urge to kill: he feels a sensation of blood washing over him until he needs to explode. “The only way to relieve the pressure is to open the floodgates — let it spill out,” he says.

Deb shows up and talks him down, unaware of the slumbering intern in the trunk. It’s a huge moment for Dexter, admitting he was about to kill and preventing himself from doing so by contacting someone. Deb tells him as such: “It makes me think you can control this.” The scene is one of many filled with emotion and stellar acting from the powerful leads this week.

The episode ends with Dexter and company working at a field operation where investigators are searching for some buried bodies a prisoner claims he wants to reveal to clear his conscience. Dexter talks with the prisoner about guilt, recovery and catharsis as Deb crosses the street to get some Frosty Swirl ice cream. The prisoner remarks on the fresh air and sunshine, then says he has one person left to kill and walks directly in front of a moving tractor trailer.

Blood spatters on Dexter’s face and the road as the camera switches to slow motion and Deb drops the cones. Dexter realizes there never were any more bodies. The prisoner just wanted to see the sunshine and the Frosty Swirl before killing himself. “He couldn’t take life in prison,” Dexter concludes, looking over at Deb, “Can I?”

This season is shaping up to be a powerful and vivid one full of emotion and connections. The dynamic between the always excellent Hall and the now-powerful Carpenter will certainly be the focal point of the coming weeks. They’ve started constructing their own code: absolute honesty and always calling when wanting to kill, so far. Will Deb reveal her forbidden attraction? Will Dexter slip up and kill again? And what about LaGuerta?

Next week, Isaak Sirko zeroes in on Dexter and the forlorn prisoner’s former partner in crime enters the fray.

king@umdbk.com