If “Homeland” were a Hollywood movie instead of TV’s best drama, it would have ended shortly after Carrie Mathison was vindicated in her long-held suspicion of Sgt. Nicholas Brody as a POW who turned against the U.S.

And yet, the Emmy winning drama with a growing audience can’t stop now; heck, a third season has been ordered halfway through the acclaimed second season.

So the question becomes: How do you keep a show and its lead characters going after the cat and mouse premise has been resolved?

“Showtime” producers came up with an answer and provided it in one of the most compelling, deeply cutting and emotional episodes thus far. That it was capped by one of the dumbest secondary stories didn’t even blunt the impact.

Assuming you’re aware of the spoiler minefield here, the episode began with Brody in custody and the interrogation about to begin. That questionable new lead investigator on the case David Quinn took his first whack at Brody, sitting prone and chained at an interrogation desk, his knees pumping wildly in nervousness – a quirk his character has had since season one.

CIA director David Estes is not happy Carrie impetuously broke what was to have been a surveillance operation, calling in for the arrest after the first drink she shares with him. This is how “Homeland” got to be such a great show: moving quickly to do peak actions other shows would have waited several seasons to reach, from having the two lead characters hook up midway during the first season to staging the big terrorist event.

Its producers are used to this tightrope walking without a net. They learned it by keeping adrenaline running on nine seasons of “24.”

It’s all the CIA brass can do to let her stay in the building as Quinn begins his interrogation, laying out the questions in such a methodical manner that it even impresses the skeptical Carrie – at least until Quinn loses his temper, pulls out a knife and shockingly stabs Brody’s hand.

The action takes us back to “24” as well, when Jack Bauer regularly indulged in torture and “enhanced questioning techniques” if there was a terrorist threat to found out.

While “24” might be seen in hindsight as an apologia for the official use of  torture during the days of Abu Grahib, there is no tolerance for it here, as Saul and Carrie rush in and Quinn is apprehended and taken away.

It might all be theater, though: Quinn sits comfortably to watch what comes next; he won’t be hauled into a disciplinary hearing anytime soon. And Carrie is in the room and tries her (unmolested) hand at the questioning.

Thus begins one of the most disarming segments in “Homeland” history – nearly a half an hour of emotional, superbly acted give and take between the giants whose acting has carried the series so far.

Rare is the TV show that has the patience and confidence to have such an extended scene of pure dialogue and emotion. It was more like a powerful one-act play compared to the usual multi-story, quick cutting of even the best TV dramas.

And yet that’s exactly what the producers needed to do if they were going to pull of their greatest trick: Finding a way for both Claire Danes’ Carrie and Damian Lewis’ Brody to continue in the series despite his being caught. They can now work together! It’s a notion so far fetched it’s as if The Fugitive’s Dr. Richard Kimball was captured at long last and enlisted in the search of the One Armed Man.

Carrie’s long talk with Brody breaks him down just as systematically she says his  terrorist captors had broken him down. And yet she begins her inquiry as if it’s one of those post relationship conversations by a scorned partner: “You broke my heart you know. Was that easy for you? Was that fun?…Look me in the eye and tell me you felt nothing.”

It’s the kind of breakup exit interview most men already dread, so it helped that he was chained there and had to listen. But Danes’ Carrie was vulnerable, and honest, and had tears in her eyes and was pleading with him.

Was it part of an act?

“Every good cop needs a bad cop,” Quinn muttered as he watched the video feed of her interrogation.

But that was before she shut off all the cameras and pretended they were all alone (she kept the audio feed on). Then she fed him water from a bottle, unshackled his hands, and spoke with concern of his lack of having someone to talk to – someone with whom he could share some truth.

“It’s the lies that undo us,” she says. “You’re drowning in lies.”

She tells him it feels good to tell the truth so she proves it by telling her own: She wishes he’d leave his family and go off with her. Not likely, but she says she feels good just declaring the truth.

She holds his hand and says she believes he’s a good man, because he didn’t set off that vest bomb, because he listened to his daughter and made a decision to come home that day and not to blow up the vice president.

“That’s the Brody I fell in love with,” she says, her eyes full of tears, his eyes full of tears too.

And then she asks the same question, without the knife: Does he know the terrorist plan against America?

“No.”

“There is a plan, right? To attack America?”

And in a surprisingly high voice, he finally breaks: “Yes.”

There comes a list of all he knows and the possibility that he could return to his life if he continues to string along the terrorist contacts and learn more from them.

Even more enticingly, Carrie tells him that his cover — should anybody wonder where he’s been the two days he’s been locked up — is that he’s renewed his affair with her. And that will be their cover for contact going forward.

Is it a deliciously perfect set up for Carrie romantically as well as professionally? Or will it be as difficult for her pretending to have an affair while in fact they are not? She takes a long gulp of white wine when she gets home as if she’s wondering over Most of Brody’s family seems happy to see him back when he arrives home with his injured hand, blaming it on a bender. Wife Jessica even buys at first his real truth: He’s working for the CIA. But when Dana comes home from a date, she’s too dazed to register much about his homecoming.

That’s because she’s been involved in her own little hell. On a date with the vice president’s son Finn, he decides to ditch the Secret Service cars following them and begins speeding through the D.C. streets. The incongruous high speed chase seems inserted as a way to give action to an episode that otherwise has none but the hand-stabbing.

Dana encourages him to go faster, as if it were some 1950s hot rod movie, and while they manage to ditch the Secret Service’s black SUV, they also slam into a pedestrian who bounces off the windshield.

Suddenly, we’re back to season two of “Friday Night Lights” – a case of when bad plotlines invade good shows.

Finn has no intention of sticking around at the scene of the accident. “If anybody finds out about this, my life is over!” he says. She finally agrees, and together they are complicit in the hit and run.

In the preview for next week’s episode, he’s already yelling at her and she’s thinking maybe I shouldn’t have broken up with my old boyfriend to go with this dude after all.

But because they’ve always got the pedal to the metal on “Homeland” the preview also indicates that that the terrorist action they’ve been trying to track is already going down.

And then what?

That’s exactly why we’ll be coming back.