The plot around Carrie Mathison thickens and President-elect Elizabeth Keane gets a moment to shine as “Homeland” hits the halfway point of its sixth season in “The Return.”

SPOILER ALERT: Do not read if you have not seen the Feb. 26 episode of “Homeland.”

The sixth episode, written by Charlotte Stoudt and directed by Alex Graves, finds an old compadre — German agent Astrid — of Carrie Mathison and Peter Quinn showing up at the very end, hopefully as a force for good. Saul Berenson turns to a Russian agent for a Coney Island exchange of surveillance dirt that gives him more reason to question the motives of his CIA boss, Dar Adal.

Dominic Fumusa’s crusading FBI agent Ray Conlin redeems himself by realizing that Carrie just might be right about Sekou’s innocence and the larger conspiracy around her. But before he and Carrie can plot their next moves, Conlin winds up on his bathroom floor with a bullet in his head.

But the emotional highlight of this eventful episode was the weighty exchange between Keane and Marjorie Diehl, her CIA-assigned housekeeper of the safe house where she’s been whisked away for security reasons after the bomb blast at the end of episode four.

The Diehl character was given a touch of menace in last week’s episode when Keane walked in to a bedroom to find her watching a political TV show hosted by an ultra right-wing Alex Jones type. But this week she winds up helping Keane thwart the vigilance of her CIA captors by driving her back to Manhattan. In the car, the two have a frank exchange that does a good job of illuminating the depth of the nation’s political divide — without histrionics or invective.

The discussion begins with Diehl acknowledging that she did not support Keane in the presidential election. We learn that Diehl, like Keane, had a son who died in a post-9/11 military operation — presumably in Iraq or Afghanistan. The lengthy exchange demonstrates how reasonable people can have very different reactions to the same traumatic event — the loss of a child.

That jolt spurred Keane to question every aspect of the governmental and institutional construct of the war on terror. For Diehl, the loss of her son made her angry at Keane’s agenda to make a big change in the nation’s foreign policy agenda. To this grieving mother, Keane’s decision was a betrayal of her son’s sacrifice.

“You made him invisible. Not just him but all of them. What they did. Why it matters,” Diehl says. She even goes so far as to express her belief that Keane is “ashamed” of her own son’s service.

Keane disavows that notion (“No. God no. Never.”) but demonstrates her anger at what she feels was a ruse to start the war in Iraq, which she supported during her tenure in Congress.

“I voted for the war. I voted to send my son and yours to a place they never should have gone, for reasons I came to understand were false and misguided,” Keane tells her.

Kudos are in order for Elizabeth Marvel (Keane) and Deborah Hedwall (Diehl) for handling a tough scene with dignity for both characters. The tension slowly rises as their conversation continues, perhaps because we are all so accustomed to the shouting matches of cable news. But these two women part with much greater respect for each other than when the ride started. Diehl sets the tone by acknowledging that Keane deserves the respect of the office that she has won even if Keane didn’t win her vote. “I’m OK with that — half the country can’t stand me,” Keane says.

Keane later articulates her appreciation for Diehl’s candor in her remarks to the waiting news media when she has Diehl drop her off at her Midtown hotel, blocks away from where the delivery van bomb went off. But in the same breath, Keane makes it clear that the latest incident has only deepened her resolve to change up the game plan in the war on terror.

“We don’t need a police state in this country to fight terrorism,” she says.

The frank talk with Diehl moved Keane to publicly mention her son Andrew, along with Diehl’s son John. “They both did their best to serve their country and face down fear,” she says. In this way, Keane stands her ground but acknowledges Diehl’s viewpoint.

If only more real-world politics could be scripted by the “Homeland” team.

A few other highlights:

• Saul has friends in all the right places. His Russian friend Viktor comes through with the evidence he needs to realize that Mossad agent Tovah and Dar Adal are playing games with him in his pursuit of the truth about Iran’s nuclear program.

Like any good Russian spy, Viktor is nothing if not savvy, wily and quotable. And he inspires a kind of poetry in Saul: “We back-channel for our bosses, turn down the temperature and keep the peace, such as it is. We don’t hold each other for ransom, or ask what we cannot give,” Saul states when Viktor presses him for payback on the favor.

“It’s obvious you are on the outside looking in. Maybe you’re not much use to me after all,” Viktor responds. Ouch.

• Peter Quinn is in such bad shape when Carrie finds him at Bellevue mental hospital that you have to wonder if he’s been drugged. Rupert Friend has had a long tour of duty in the makeup chair to get the battered-and-beaten effect just right.

• Ray Conlin checks out in this episode but not before he gets a long last hurrah with his visit to the weird data-mining center in Virginia where more connections to the Carrie of it all are uncovered. The click-click-click of the sound mix and harsh fluorescent lights gave the sequence a Kubrickian feel.

• Franny Mathison doesn’t seem to hold the drama of last week’s episode against Quinn, as she inquires about his well-being. Max the ever-reliable computer tech is back again to help a fritzed-out Carrie regain a feeling of security at her home. The final shot of Carrie’s silhouette with gun in hand watching Franny sleep underscores just how hard it is to be a Mathison.