'NCIS' Star Reveals How Mark Harmon Helped Her Feel Like Part of the Cast

COLLIDER: With the 500th episode of NCIS, the series has now surpassed series like Grey's Anatomy, Family Guy, and classics like Bonanza. What do you think it is about NCIS that has made it such a mainstay, not only on television but with the fans that continue to watch the show and even rewatch it where it's in syndication?

DIONA REASONOVER: It really is the fans. I can't give credit to anyone but the producers, the writers, and the fans. Really and truly, they are keeping it alive. Every time they send us theories, or they're DMing me, like, “Is such-and-such coming back?” I know that they're tuned in, and hey, thank you. Thank you for watching, and thank you for making this show great, amazing. Thank you for making this such a cool vehicle to be a part of.

I also think it's the showrunner, the writers. They've crafted these amazing characters that have surpassed my imagination of what I thought was possible. I can't imagine writing 500 episodes… It's been a really cool place to be. I just think it's such a special and wonderful show. And like I said, a lot of that is really due to the writers and definitely due to the fans, who are loyal.

How 'NCIS' Has Made Fans Out of Its Cast Members

I've been an NCIS fan since it was a backdoor pilot on JAG all those years ago. I've loved hearing what everybody's own connection to NCIS was before they joined the show. Were you somebody who was watching the show beforehand, or did you join and then become a fan?

REASONOVER: I actually joined and then became a fan. Not only have I brought myself into the fandom, but I've also gotten my wife into the fandom and my mom and my extended family into the fandom, which is great. But it also means that whenever NCIS is on in real life, I'm not allowed to talk. I have this fantasy that we'd be watching the episodes, and I'd be pointing out like, “Oh, this camera angle came up because the director did it, or the writers suggested X, Y, and Z,” but instead my family is just like, “Could you not talk? You're interrupting my show.” And I'm like, “I'm on that.” They're like, “Yeah, we can talk to you any time.”

They're like, “No Mystery Science Theater 3000 here.”

REASONOVER: Yeah, truly! I know. I thought we were going to have a whole back-and-forth. I thought it would be like the director's cut. “Here's the actor’s cut.” No. They're like, “Cut it out.”

I love that. Then, looking back to when you joined the series, what do you remember about the audition process and your first days on set?

REASONOVER: I recently got sent my audition, actually. I got a chance to see it for the first time. That was trippy. It was a lot. But you know what? I can see the beginnings of Kasie because I'm just rattling off all the information. It's a scene with Gibbs that I was doing, and it was really fun. It feels really different for me in a way that I'm like, “This is cool!” It's cool to see those early little tendrils of the character.

I remember that the room felt really warm, and when I walked in, it felt like everybody wanted me to succeed. It doesn't always feel like that. Sometimes it feels like it’s you against the audition, and you're almost always wrong, because usually — and I'll say this to anyone who wants to be an actor — people want you to succeed. People want you to be good because then they can say, “We did it. We're good. We can go home.” But the truth of the matter is that it felt like one of the warmest, nicest, most “we want you to knock us out of the park” rooms. It just felt like playing, and it was great. And even in the early days on set, they felt like that. It felt like I walked in and everybody was really nice, everybody was really kind, and I just got to play.

If my recollection is correct, you joined Season 15 in 2018, correct?

REASONOVER: Sure! [Laughs]

I think I’m correct on that. The years have all become a blur, but about eight years of your life have been on that set? What has playing Kasie taught you about yourself?

REASONOVER: That's a really good question. I think I’ve used more curiosity in my life. That is the thing about Kasie, she is infinitely curious. She's infinitely wanting to help. I constantly want to help, but also, often, I don't know what I'm doing. So, it's fun to get to play someone who's really confident, who's really strong, who's not afraid of just stepping in and kind of overstepping a little bit. She's not afraid to just get in there and be like, “Hey, listen, I know you've been doing this, but check out this thing that I've been working on,” which is amazing to get to do.

She's such a nerd and a science person. Has it made you delve into some of her interests and her strengths and learn more so that you can improv if you need to or pick up something really fast?

REASONOVER: Ha! Improv. That's real fun. That's a real fun idea. No. I wish. It's such high-level stuff. The way I figure it, this is what I'm going to start telling people: If I could Google it, the criminals can Google it, too. So it's probably best that I don't know. You know what I mean? Like, if I had to catch a criminal using just a sock and looking through microscopes, the criminals could Google it too. So maybe it's best that I just leave it to the professional writers there.

What Are Some of Kasie's Best 'NCIS' Plotlines?

Thinking back across the years, there have been so many interesting plotlines and storylines. What are some of the ones that still stand out to you that you've gotten to explore with her?

REASONOVER: Well, first, I just want to say I sort of jumped ahead on that question. I thought you were going to say some of the favorite plotlines, and I was just going to start listing my favorite episodes, which I'm going to do anyway. I think they're great. I just watched “Devil's Triangle” in anticipation of a reading that we did — so good! I loved “She.” That was such a great, strong episode.

Then, as far as Kasie and things that we've gotten to explore, Marco Schnabel wrote a new script that we're just working on right now, and it's been really, really fun to play, and you'll get to see that. I know people always say, “you'll get to see this character in a new light,” but you'll get to see some of her doubts, some of her fears, which, like I said, I don't often get to play that because usually by the time I'm coming in, I'm going to know exactly what's going on. Marco's given her a chance to be self-doubting in a way that I love and that feels very relatable. He also wrote “Lifeline,” which is the one where Kasie does Walk a Mile day, and she overhears a murder. He wrote some very cool things, and so this feels like a really nice continuation of that.

I love that when you get those throughlines with writers coming back and continuing little things that they needed, and you get to see the plant grow with the character. I was looking back through clips from seasons past to refresh my memory, and it reminded me of how much Kasie and Ducky had such a sweet connection. Looking back at that, what was that like getting to work with David [McCallum]? He was such an incredible actor and also such an iconic character on NCIS.

REASONOVER: Definitely. Absolutely. I learned a lot from David. He was the consummate actor, and to get to see someone who had such a lengthy career, there's a lot of wisdom to be gleaned from that. It was always really fun. He came in with ideas, ready to go, ready to bounche them off of you. It did feel like a continuation of that idea of play with David. So, I definitely miss him dearly, and I know a lot of my cast mates do as well.

It's been interesting on the podcast. In an ideal world, we would have gotten to interview David. But we get to hear Brian [Dietzen] a little bit talk about their relationship. It was interesting coming into that from an inside perspective and getting to hear what that relationship was like with them. It's good. You should listen to the podcast if you haven’t.

Oh yes, I have. I'm so excited for the podcast. I love any time a series starts to delve into episodes and look at them with the cast. What has that experience been like, getting to see this through? Has it changed how you look at the series at all? Obviously, you were talking about wanting to dissect episodes with your family, but now you're getting to do that with the fans.

REASONOVER: I know. It's very cool. Here's a fun, interesting little tidbit. Originally, it was going to be a recap episode show, but as you see from my patch, we're at 500 episodes. It's going to be quite a bit before we get to Kasie on screen, and we decided to just do more interviews so that we could do this, so that we could have this more inside baseball with the cast, with the crew, with the writers, with the people who are shaping these episodes. It has changed the way that I see the character, because all of a sudden I get to watch people's reactions when I say, “Yeah, this is what I meant,” and people go, “Oh! That's really fun!” Because now I get to take that information on, like, “Okay, what's clear? What's reading? What's not?” and put it directly into what I'm doing. It's like a real-time actor salon. It's very fun.

How Mark Harmon Made Diona Reasonover Feel Welcome on 'NCIS'

Listening to that makes me think: I interviewed Sean [Murray] last week, and he talked a little bit about the things that can change on the day and then can influence character traits and character things that lead down the line. Have you had any of those moments where, when something happens in rehearsal, somebody’s like, “That's really good. Let's keep doing that,” and it continues with the character?

REASONOVER: Oh, for sure. Yeah. Maybe littler things. Not like, “What if we put the dead body here?” Not like that. But with some of my favorite writers, there is this spirit of play, this spirit of, “Oh, hey, that inspired me.” And even if it doesn't inspire in that moment, if we can't change it in that moment, because you can imagine there's a ton of moving pieces, so someone’s saying, “No, we’ve got to keep this.” That's fair, and I understand why, but sometimes later on, it tells them, “Oh, this person is really good with this,” or they really picked that up really quickly, so maybe let's incorporate a little bit more into the character.” I think the writers are writing what they see for the most part.

It's so important to have that kind of collaborative set, especially with a show that's been on for so long, because everybody feels like they're settled into their characters, which I love. I am curious to know, what are your favorite types of scenes to film?

REASONOVER: Well, me and Sean Murray can always knock it out of the park. You give a Kasie and McGee scene, and we're like bang, bang, boom, boom. It's great. So, that's always fun. Well, it's hard because now I realize I'm just gonna start listing everybody. Obviously, I love scenes with the main cast. It's also really fun to do guest star scenes, which I don't often get to do, so when those happen, that's really fun to do.

Especially when you've been on a show for quite a few seasons, when you have those day players and guest stars that get to come on, they tend to look to the main cast for, “How is this experience going to be?” How has that been for you getting to be that person when there are guest stars that you get to interact with, who look to you?

REASONOVER: Man, I'm just trying to be as nice and as kind as the cast was to me when I got there. I still have memories of Mark [Harmon] clearing my lunch tray for me, Sean and Brian offering to run things with me, and Will telling me jokes when I was nervous. I just have all these great memories of the people who were there, who made me feel welcome, and I'm just trying to do that as much as possible. I don't clear as many lunch trays as I should. I'll cop to that.

[Laughs] Something to resolve to do this year.

REASONOVER: I gotta work on my wrist. My wrist are like, “Oh! You didn't finish your corn!”

I love that. My last question for you is, if you had to imagine NCIS in another 500 episodes, what do you think that looks like? Is Kasie still around? Is she still hustling?

REASONOVER: We have to go to the place we've never gone — NCIS: Helicopter. “Every scene takes place in a helicopter, a separate helicopter, this helicopter flies up to this one!” Kasie is not there because she's on the ground. That's the next 500 episodes.

I love that. I feel like Michael Bay needs to guest-direct those helicopter episodes.

REASONOVER: Why not? Why not? [Laughs]

NCIS airs Tuesdays on CBS and streams next-day on Paramount+.