The Blacklist's two-hour Season 4 finale is going to feature a big showdown between Red Reddington (James Spader) and Mr. Kaplan (Susan Blommaert). But will it be a fight to the death for the two former partners-in-crime? Having FBI Special Agent Julian Gale (Enrique Murciano) hot on both of their tails will only complicate things for Red and Kate, who may find themselves needing to join forces once again in order to protect each other from a common enemy.

And, amid all the action, it's possible that the finale will include even more bombshell revelations that will illuminate the history that ties Red, Mr. Kaplan and Liz Keen (Megan Boone) together.

TVGuide.com chatted with Blommaert ahead of the season-ender to see what's in store for Red, Mr. Kaplan and Liz -- and whether Mr. Kaplan's desire to get revenge against Red is outweighing her desire to protect Liz.

Assuming the finale is a final showdown between Red and Mr. Kaplan, what can you tease about it?
Blommaert:
I know that, because of Red and Kate's history, [Mr. Kaplan is] a formidable foe. The arc of the character has been so interesting and a lot of fun, and a real challenge to play. But I think it's a challenge a lot of people will recognize. I think many of us have walked that fine line between love and hate, and this has been a true high-wire act, this one. I, as Kate, promised Liz's mother, Katarina, that I would protect her daughter with my life, and I intend to keep my promise. We'll see where that takes us.

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When did you find out Mr. Kaplan's backstory? What was your reaction?
Blommaert:
I really didn't find out what her backstory was until I saw that script, which was pretty shortly before we shot that episode. I certainly knew some things about the background, but not the entire storyline of the backstory. As an actor, I had created a backstory for myself, of course, just something that I could land on when I needed to, or have a base for where I was going to go, that I made up myself as an actor. But when I saw that script, I was surprised that there were quite a few things in the script that I had kind of come up with from what I had done previously, just from knowing the character for the amount of seasons I've been doing it. ... But I have to say that I could never have written it as brilliantly as they wrote it. It was an exceptionally good script, I thought, and it also just had wonderful surprises for me. Like, the revelation of why my name is Mr. Kaplan was just so simple, so tragic and so right.

What percentage is Mr. Kaplan motivated by getting revenge against Red, and what percentage by protecting Liz?
Blommaert:
That's a very, very good question, and something that I as an actor have had to work on in the arc of this character and where we've come to this point. It really, for me, has been almost like walking a tightrope. I'm not quite sure which way, if I fell off - and I would stumble certainly, on occasion - which side I was going to fall off on, whether it was the love or the hate side. I think there's been a little crossing back and forth on that line. I think that's true for both Reddington and Kate Kaplan. It's like a family feud, and nobody wants to cry uncle. But there is that family feud element, where you're torn between how much you love and how much you hate.

Will Mr. Kaplan and Red be able to put aside their differences and team up against a common enemy, Julian Gale?
Blommaert:
There's always hope. That's all I'm going to say about that. There's always hope, no matter which way you look at it. But it is interesting the question you ask, about the percentage of revenge and the percentage of concern for Liz's safety. I knew that Raymond would see what I did, helping Liz fake her death, as a betrayal. But I believe that it actually was keeping my promise. Once I realized I had to make a choice, once I felt that he had lost sight of that goal ... to protect her, there's danger there. So, I feel like throughout this, there's been such a combination of revenge for being shot in the head ... but also, I don't believe that it's ever totally and only been about revenge. It's also been about keeping my promise to protect her safety. ... Whichever moment it happens to be within the action could be a little more revenge or a little more safety. But always, the goal has been a combination of those two, I think, for Kaplan. ... The love-hate there is very real, and almost a moment to moment situation.

Do you think Mr. Kaplan and Red are both well-intentioned when it comes to Liz?
Blommaert:
Yes. I believe that they both believe that they have her best interest and her safety and her happiness at the root of what they do.They have not come together as far as how that is accomplished. ... Kate thought that [Red] had lost sight of doing that, and the very fact that she was in his life was what was causing the danger. And whether [Red] recognizes that or not ... is questionable.

Is there anything else you can share about the finale?
Blommaert:
There are going to be some pretty great surprises in these last two episodes for the audience, in a lot of the background moments and the relationship. I think that it's going to be a really good rollercoaster ride. Hopefully everybody'll just fasten their seat belts.

The Blacklist's Season 4 finale airs Thursday at 9/8c on NBC.