We’re all counting down the days. Castle Season 8 premieres later this month, and there’s a lot we can look forward to.

I spoke with two-time Emmy and Golden Globe nominee Susan Sullivan, who plays Martha Rogers on Castle, about the upcoming season and what it takes for a show to make it this far.

As it turns out, something told Sullivan the show would last eight seasons. “I did predict it, I like to say, to give myself a little pat on the back. There was some silly little interview, I don’t even remember what it was exactly. This was in Season 4 or 5, and I said ‘this show will go eight seasons!’ Didn’t it?! Don’t ask me how I know these things,” Sullivan laughed. “I was sort of being silly. Anyway, there you go!”

With Sullivan’s experience in the industry, she’s learned what it takes for a show to last. “I was on a couple of other long-running shows [Dharma and Greg, Falcon Crest], so you sort of get a feel for the ingredients that make a show work in the long run,” Sullivan said. “Although, the whole business is changing so radically now, because there’s just so many outlets, and so much stuff you can view, and so many places you can watch it.”

Sullivan believes Castle has those very ingredients, which have contributed to the show’s success. “Well, I think it’s the chemistry of the leads. I think it’s the chemistry of all the characters working together in a balance,” Sullivan explained. “But essentially, it’s the two of them [Nathan Fillion and Stana Katic]. And it’s a little off-center. He [Nathan Fillion] has this kind of quirky, funny quality. He has a huge following. He’s a lovely guy. I’m completely crazy about him, which is really nice. It doesn’t always work out that way, as you can imagine. You know, they’re really both wonderful actors. So there’s that component. But you know, because you’re a writer, you know that you don’t have it if it’s not on the page.”

This season, one of the major changes for Castle is that it now has two new showrunners, Alexi Hawley and Terence Paul Winter. “Andrew Marlowe and his wife, Terri Miller, they just – it was enough. It’s really a grace note in life if you can know when to leave, and this was just the right time for them to leave,” Sullivan said. “So there are new writers, and they have their own new take on it. They want to, the way all artists do, imprint the show with their particular style. So, it’s the same and a little different. I think that’s always good, although people are so resistant to change.”

Sullivan then went on to explain some of the ways the show will be different, but she said those differences aren’t major. “Basically, it’s still a procedural. There will still be a mystery that you follow for each episode. I think it’s a little quirkier and maybe a little bit more fun. Then, I think it also has an underside of darkness that’s kind of intriguing.”

At its heart, though, Sullivan said that Castle is about the love story between Castle and Beckett. “It’s always been a love story about these two people and their progression of commitment and so on. So, that will continue and be explored. What’s more interesting than that? It’s what we’re all struggling with on the planet – trying to connect and feel that unconditional love. And not make it about yourself, but about the other person.”

We know there’s a particularly big change for Beckett coming up, but Sullivan also gave us a few other hints as to what we might expect during Season 8. The first is that Alexis (Molly Quinn) will be a more integral part of the story. “I think it’s nice that darling Molly Quinn is going to have a little bit more to do and grow up in quantum leaps. Of course, she has already grown up in quantum leaps on this show. I can barely believe this little girl that we started out with is now this woman who is giving me advice. Which, of course, I resent [laughs]. No, I don’t. She’s one of these wise old souls. She’ll be more involved with the mysteries, which I think will be fun for the audience and her.”

We can also expect some fun things from Ryan (Seamus Dever) and Esposito (Jon Huertas) this season. “There’s kind of little dances between the relationship of the boys. The boys – I call them the boys,” Sullivan said. “They’re always fun. And they’re good friends. They socialize with their wives, and they travel together. So it’s fun for them to have this little dynamic in their relationship, which I think is great.”

Sullivan talked about Martha’s character as well, including her new found love for social media. “My character is pretty much the same, although I started tweeting this season, much to my surprise. And I really like it! I’m having a very good time, because I found something that makes sense for me, Susan Sullivan, who likes to give unsolicited advice to people,” Sullivan explained. “Believe me, they don’t want it, but I give it to them anyway. This way, they can either take or not take it, or look at it or not look at it. So I’ve been doing that, and I pitched to the writers that they do that with Martha on the show, because she had this success with this Broadway show, and the Twitterverse acknowledged her. I would think she would be tweeting her fans, and trying to build a fan base, and all those things that actors do. So that’s my intriguing thing. It may only be intriguing, Ashley, in my own mind, but there you have it! [laughs].”

Martha’s character is certainly one we’ve grown to know and love, and Sullivan said the inspiration for her character comes largely from her mother. “I used a quote of hers in the first episode when I was sort of, when my character was a little but more of a coach for people. My mom would say this: ‘You is who you is, and if you ain’t who you is, who is you?’ That was my grounding in my mother’s wisdom and her silliness. Which is a delightful combination, I must say, because wise people can be rather tedious. And whimsical people can get on your nerves too. But a combination of both sort of grounds you. That was certainly what I based the character on. My mom died in 2011, so she died in the middle of all this. But she got it. And I think she was pleased. In fact, I know she was.”

But there’s another thing that helps Sullivan get into character. “That damn wig! When I put that damn wig on my head, Ashley. I don’t know if you’ve ever had this experience, but it’s really strange, and I’ve been an actress for a long time,” Sullivan stated. “I’m looking in the mirror, and the hairdresser puts it on my head, and I’m like, ‘who is she?!’ Then I remember my mother’s quote. It’s always shocking. So that helps me. I remember an actor friend saying to me, ‘I don’t really know the character until I’m wearing his shoes.’ So, I don’t really quite embrace the total Martha until I have all my jewelry and my red hair.”

Sullivan also shared which episode she remembers as being the most fun to do, and her answer wasn’t surprising at all. “It was last season, and it was the episode in which Martha is nervous about the play opening and she’s reciting the first line, ‘Is he dead,’ over and over again [“Dead From New York” S7 Ep22]. I loved that. And I loved the payoff with Nathan when he comes in, and we both stand up and say, ‘Is he dead?!’ That was my favorite.”

Behind the scenes, Sullivan said it’s a “pleasant place to be.” She does, however, prefer the loft setting to that of the precinct. “I love being in the loft. I think they have me moved out now, but I don’t have a home of my own. I’m in the loft a lot, because that’s the most comfortable fit. The precinct is not a comfortable fit. Everything is kind of hard. The loft is kind of soft and cushy, so that’s the kind of job I have, Ashley. Soft and cushy [laughs].”

On a more serious note, though, Sullivan is truly grateful for the years she’s spent on Castle. “The whole experience has just been extraordinary,” Sullivan said. “I am practicing the wisdom of gratitude on a daily basis.”

Check out the promo for Castle Season 8 here:

Castle returns for Season 8 Monday, September 21st at 10/9c on ABC.

*Edited for space and content.