'NCIS': Diona Reasonover on Knight's Awkward Holiday Get-Together and Exploring Kasie's Love Life (Exclusive)

The actress and writer previews Monday's holiday episode with ET. Plus, watch an exclusive clip!

It's Thanksgiving time at NCIS, which can only mean one thing -- something's about to go wildly wrong. 

On Monday's episode, appropriately titled "Turkey Trot," Kasie (Diona Reasonover) is invited over to Thanksgiving lunch with Knight (Katrina Law) and her sister. At first, what begins as a typical awkward holiday get-together quickly goes south when Knight's sister, Robin (guest star Lilian Bowden), breaks some surprising news and the group finds themselves put in a precarious situation that connects to the larger case the NCIS team is investigating.

Reasonover, who co-wrote the episode, offered insight into how the idea for the storyline came to be. "I really love holiday movies... But everybody gets along a little too nicely for family," the actress told ET while previewing the hour. (Watch ET's exclusive sneak peek above.) "I just think it's so interesting to get to explore families and what they're really like. You can love someone even if you don't always like them. And to get a chance to explore that with Knight was something I was really excited about. We wanted to show the thing that I think a lot of people experience, which is they do not have a Pinterest-perfect holiday."

Ahead of the episode's premiere, Reasonover discussed Kasie's evolving role on the team in season 20 amid Gibbs' absence, writing a NCIS-ified Thanksgiving episode and what she hopes to explore with her character in a potential 21st season (hint: love!).

ET: You're in the thick of season 20. How are you feeling as filming has progressed?

Diona Reasonover: It's been a really fun season. I think a lot of people, me included, were worried. This is our first season without our wonderful leader, Mark [Harmon]. But it's also been cool to explore new characters and new relationships and kind of figure out all these new rules. So it's been thrilling and it's always nice to do something different, you know what I mean? I think that's kind of why you become an actor. You get to do something different every day.

You mentioned this is the first full season without Mark. How has that transition been and how do you think your role among the cast and then as Kasie has evolved as a result?

I think Kasie has become much more involved, but Mark is still very involved and he still is an EP. He still comes up to set. He actually came up to tell me how much he loves the script, such a sweetie. So that's been really good and I really enjoy getting to know Parker's character and finding all those little edges and also all those little pastries that I've been eating because his character brings pastries.

Speaking of pastries, this upcoming episode is set on Thanksgiving Day and you also co-wrote the episode. How did this come about?

I actually have written episodes of TV before, so I was really wanting to write an episode of NCIS, but I was worried about, "Oh, would it be stepping on toes? Would it be strange?" And then Brian [Dietzen] got to write one with [writer] Scott [Williams] last year and I was like, "Oh wait, what? That's an option? OK, definitely want to do that." So I asked [Scott] if I could and everybody was so receptive and so excited about it that when the time came, Scott said, "Just pitch me ideas. I want good ideas." We talked and I pitched him an idea and he said, "Great, no, not that one." And I said, "OK." I pitched him four more and finally we came up with this one because I think we both really wanted to explore Knight's character, but I also really wanted to see what Knight's sister was like.

Sonja Flemming/CBS

What was the experience like putting pen to paper for NCIS? How is it different from writing on a comedy?

I have to be honest, the writing part, easy. Feels like home. Love it. I was not worried about that. Now what I have never done before is had to act on something I've written. I've actually never done that before and that was completely different. I was so embarrassed. I was so busy sometimes listening to other people because it's a really different process, listening as a writer and listening as an actor, and I would forget my line. I was like, "Line?" Messing up my cues. Because I have six different versions of this scene in my head from all the rewrites. But it was also really satisfying.

Were you finding yourself trying to turn off that writer's switch when you were also in the scene? How did you balance that? 

Oh, it was absolutely ridiculous. Scott Williams luckily is a great co-writer and he would always tell me, "Go act." And I of course could not. I was like, "But I must continue to worry about small things and did I write this correctly? Did I convey my point correctly?" But between him and our really, really great director, it was very apparent from the jump that things were in good hands and I literally could go act as much as I was going to allow myself to.

What can you set up for viewers when they watch the episode?

I really love holiday movies, Christmas movies. But everybody gets along a little too nicely for family. And not that I don't, but I know so many people and I've seen so many times, holidays are when everybody's the most stressed. All of a sudden, instead of cooking for two or four people, you're cooking for 24, everybody's a little bit snappier, a little bit hungrier because you haven't eaten. I just think it's so interesting to get to explore families and what they're really like. You can love someone even if you don't always like them. And to get a chance to explore that with Knight was something I was really excited about. We wanted to show the thing that I think a lot of people experience, which is they do not have a Pinterest-perfect holiday. The food comes out burned or there is no real picture-perfect food and people fight. And of course then, it's NCIS. There's still dead bodies. Did they tell you how bad I am with blood and gore?

I was not aware.

Yeah, our prop department is a little too effective and sometimes I just have to pop my contact lenses out, so I can't see. So when we were writing I was like, "OK, no gross dead bodies."

This isn't the perfect Thanksgiving get-together that takes place this episode. Without spoiling anything, things go awry quite quickly. 

Knight's sister is in town and we've never seen any of her family. Kasie gets invited along to hang out with Knight's sister and it immediately becomes clear that the two sisters don't get along. They argue. And that argument kind of becomes central to the story because it starts to intertwine with the case in a really cool, fun way. I think we get to see Jessica Knight in a way that we've never seen her before. We get to see her knocked a little bit off-kilter because the emotions have to take over in a way that we don't normally get to see. I'm very proud of everyone involved in the episode, especially Katrina. She would absolutely murder me if I said this, that she really, truly moved me and I'm so proud that I get to work with her.

I felt for Kasie in this episode. Can she just have a nice night and not get into life-threatening situations all the time?

Absolutely. I will be the one to spoil it. This is Kasie's third hostage episode. She cannot get a break. Originally, when I was pitching some ideas, I had mentioned to Scott, "Let's do Knight and Jimmy and then meet Knight's sister." And then Scott, who's been doing this for 25 years and is infinitely wise knew right away that we already had a Knight and Jimmy episode in the pipeline. He said, "Let's do Knight and Kasie." I was like, "Please, please, Kasie's going through too much. Let this woman just have a nice Thanksgiving alone." And he was like, "It's got to be..." But he was right because you get to explore a sister dynamic two different ways because you get to find out how close Knight thinks she and Kasie are, but also you get to explore Knight and her sister.

Is there an episode down the line that you are really excited for that fans should circle?

I don't have a particular episode right now, but I am really wanting -- it's not this season -- the next season we start to explore a Kasie relationship. I think that is going to come. I can't promise it, but I'm like, "OK, I want to see the episode where Kasie goes on a date," even if it does not work out. I just want to see that. It's time, it's time. Kasie's got fashion sense, she's funny. Come on, let's get her with somebody, you know what I mean?

NCIS airs Mondays at 9 p.m. ET/PT on CBS.