It’s been a harrowing year for Susan Blommaert’s Mr. Kaplan on NBC’s The Blacklist, and it’s not over yet.

In fact, Blommaert jokes, she may need another bottle of wine to get to the finish line.   

The Blacklist season ends Thursday with two episodes (9 and 10 p.m. ET), titled “Mr. Kaplan” and “Mr. Kaplan: Conclusion.”

Those titles reflect the fact that Blommaert’s Kathryn Nemec, a/k/a Mr. Kaplan, has engineered what could turn out to be a High Noon-style showdown with her former boss and pal, Blacklist main man Red Reddington (James Spader).

For decades she was Red’s “cleaner,” the person who made sure nothing could connect him to a body count that was heading toward triple digits.

Then he shot her in the head and left her for dead in a muddy field, which changed their inter-personal dynamic.

She somehow lived and she’s not in a forgiving mood.

“Your biggest threat is the person who knows the most about you,” says Blommaert. “She literally knows where the bodies are buried. That makes her a formidable foe.”

After a Blacklist season studded with intriguing twists that finally revealed much of the show’s mysterious backstory about the relationship between Reddington and FBI agent Elizabeth Keen (Megan Boone), Blommaert admits she didn’t know Mr. Kaplan would become so central. 

“TV is an interesting business,” she says. “You audition with a couple of little papers in your hand, and if you’re lucky, you get to say those lines in the show.

“Then once in a while you get to do more. I knew this could be a great character, but I had no idea she would go this far. It was a wonderful surprise.”

Mr. Kaplan, like several other Blacklist characters, embodies contradictions. While much of her work requires cold blood and little apparent empathy for human life, we learned this season that her overarching motivation is seemingly admirable.

Many years ago she promised Elizabeth’s mother that she would do whatever was necessary to protect then-young Elizabeth. Teaming with Reddington was the way to do that, because for different reasons he felt the same imperative.

When Mr. Kaplan finally did something Blommaert says “she knew Red would interpret as betrayal,” it was because she decided she had strayed from her mission. 

“She was going back to doing what she does,” says Blommaert. “Protecting Elizabeth. And she does it well.”

That’s an impressive feat for a woman of Social Security age in a world where merely staying alive is remarkable.

“She’s a badass,” says Blommaert. “A real badass. There are so many nuances to this character, which is why it’s great to have had the luxury of being able to grow.

“When you have a guest role, it’s like being dropped into a show out of a helicopter. Getting this kind of character is like having your own private jet.”

That’s one reason Blommaert says she relished the grim post-shooting scenes, when Mr. Kaplan was rising out of the mud, groping for her shattered glasses and crawling for help with a bullet wound in her head.

Not classic “ready for your closeup” moments.

A double did the first scenes where Mr. Kaplan stirs and viewers realize she survived. After that, the 69-year-old Blommaert took over. 

“The mud, the water, the way she looked,” she says, “I wanted to feel and understand that. You don’t want to do something stupid and dangerous when there are well-trained people who are so good at those kinds of scenes, but here I think it was helpful to do it myself.

“And I hate to say it, but it was kind of fun.”

Another nuance of Mr. Kaplan, fully unveiled this season, is that she’s a lesbian.

“I don’t think it defines her,” says Blommaert. “It doesn’t fully define anyone. But it helps explain her, her drive and her passion. The writers have done a beautiful job.”

She also likes the subtleties in the relationship between Mr. Kaplan and Reddington, even now.

“I always believed there’s a fine line between love and hate,” she says. “They have a long, deep relationship, and I don’t think it’s possible to totally stop loving someone you once loved.

“On the other hand, maybe that also fuels the intensity of your desire for, in this case, revenge.”

Revenge has been an unavoidable part of the drama building to Thursday’s finale – which could in turn help set up the show’s just-confirmed fifth season. 

Blommaert says she’s still focusing for now on the end of this year, since she hasn’t yet seen the last two episodes.

She recalls the episode earlier this season in which Mr. Kaplan’s backstory – the promise to Elizabeth’s mother, a romantic tragedy, the origin of her name – unfolded with a younger Mr. Kaplan, played by Joanna P. Adler (right.)

“The night that episode aired,” Blommaert says, “it happened that my family was out, so I was alone in my New York apartment. I remember sitting there with a bottle of wine, thinking that watching someone else play your character could be terrifying.”

Happily, it wasn’t.

“After the first two scenes, I knew it would be fine,” she says, noting that she and Adler are long-time personal friends from many meetings and conversations at casting calls.

That doesn’t mean there won’t be another bottle of wine on Thursday. But the truth is, things so far have worked out more happily for Blommaert than for Mr. Kaplan. 

“The Blacklist,” she says, “has been a great show to work on.”