"Castle" begins its fourth season on ABC on Monday (September 19) night, but the normally breezy crime dramedy picks up in a dark place in the aftermath of last spring's fairly shocking finale. 
 
Ruben Santiago-Hudson's Captain Montgomery? Dead.
 
Stana Katic's Beckett? Shot and seemingly barely clinging to life (not that anybody anywhere thinks Katic is done on the show).
 
This upheaval results in a brooding and introspective Richard Castle (Nathan Fillion), a side of the normally witty and charming write-turned-police-groupie that viewers normally haven't experienced.
 
The busy Fillion carved out a few minutes to chat with HitFix about the temporarily somber Castle, the big answer he's hoping to learn this season and even a little bit about that new movie that sounds a lot like a FOX series he did a few years ago...
 
Click through...
 
HitFix: First off, I can't be the only one seeing all of the promotions for "Drive" opening this weekend and thinking that you already made that one?
 
Nathan Fillion: [Laughs.] I tell ya... I had a great time doing "Drive." I thought it was it was a very cool show, kinda edgy kinda cool show. I just wish it had a chance to take a toehold. I'm gonna say that "Drive," this movie, looks even more exciting and more edgy. 
 
 
HitFix: Very generous of you.
 
NF: Well, you can do things in the movies you can't do on TV.
 
 
HitFix: I watched the "Castle" premiere the other night and I was shocked by how dark it was. When you got the script and you were shooting the episode, did you miss the misecracks at all?
 
NF: Hmmm... No. You know what? I love "Castle." It's a great show. I always say about "Castle" that it's easy to like, because it's light-hearted and it doesn't take itself too seriously. In a lot of ways, yes it's a TV show and we have to suspend disbelief allowing for a murder mystery writer to actually tail police and put on a bulletproof vest and enter very dangerous and illegal situations, but in a lot of ways, it's very realistic, in that I met a lot of homicide cops when we were in New York filming the pilot for "Castle." These guys came around and we got to chat with them, hang out with them, spend the day. They're not brooding, haunted people, tortured by their job and murder. They are very funny. They're very funny, very relaxed, very light-hearted. It's just that all of their stories start with, "So this guy gets killed..." 
 
It's much like real life. You know, life is good for a lot of people, but every once in a while, it has its dips and its falls and in real life, people do die. On "Castle," Ruben Santiago-Hudson's character, Montgomery, he dies. That's real life, with real police. There is real danger. I don't think we would be honoring their job if we didn't touch on that danger. That's a dangerous job.
 
 
HitFix: So by that token, had you been looking forward to do this side of the character and of "Castle"?
 
NF: Like anybody, I think people have to grow up a little. Some very serious things happened. Castle is very much a child at heart, but he is an adult. He's a full-grown man and he has to deal with adult things occasionally and that's real life.
 
 
HitFix: I'm not spoiling anything, I don't think, by saying that Beckett survives...
 
NF: WHAT?!?
 

HitFix: But that the dynamic between Castle and Beckett changes fairly significantly. How would you define the new status quo?
 
NF: Every season there seems to be a new reason why two people aren't together. I think that's also very much real life. I think we've all had relationships where you think, "I really ought to be with this person, but I'm in a relationship" or they're married or what have you. For these two right now, both of them are hiding the truth... Castle has been presented with the fact that if she is to delve further into her mother's murder, she will be killed, so he can't tell her that, because that will only drive her further, so he has to hide that fact from her and keep her away from that case. So you have two people who are hiding the truth from one another, having to hide how they feel about one another. How's that?
 
 
HitFix: That works. But for you as a fan of the show that you're on, how do you feel about the pace at which Beckett and Castle have moved along towards what we have to assume will be inevitable?
 
NF: Not uncommon. Realistic.
 
 
HitFix: Do you have any favorite ways that other shows, or shows that you've been on, have handled this sort of unresolved tension?
 
NF: Well, I like personality conflicts. So rarely are two people exactly the same and if they are, they probably drive each other nuts. I think you need to find something that completes you. Whatever it is that's missing about you, I think you need to find that in somebody else. I know so many couples that are so successful and so polar opposite, in certain ways they're very much alike, but in other ways, polar opposite. I think that makes for a successful pairing. So I like seeing personality conflicts. We've all talked to a friend and said, "Oh yeah, how's that girlfriend of yours? Is that working out?" and it's like, "Oh, no. I had to break up with her." And then the reason is ridiculous. It's "The way she slurps her soup" or "She interrupts when I'm talking." And the relationship is over because of these little personality conflicts, these little tweaks. I love that.
 
 
HitFix: This was a dynamic that was introduced early on, but I feel like it's gotten better subsequently. Was there an episode or moment at which you felt your chemistry sorta clicked?
 
NF: I think that these people have chemistry right off the bat. I think that's what started the relationship, that they have an obvious chemistry, but there are things about each other, certainly that Beckett can't stand about Castle, and there are things about Beckett that confuse Castle. She is really wrapped up in his mother's murder. Castle has never known his father, but it doesn't bother him. He doesn't care. I think Beckett takes a lot of things to heart. If Castle does something that upsets her, it really aggravates her, whereas I think so many things happen to Castle, life kicks him in the nuts a lot, but he doesn't notice. He doesn't really care. He doesn't really care if he ends up looking stupid. He doesn't notice it and I love that quality about him. 
 
 
HitFix: In the premiere, you have two terrific scenes with Molly Quinn. Gotta ask: Has she always been this good?
 
NF: Always. I sat in on a lot of these auditions. I read with a lot of girls to come in to play Beckett, to come in to play Martha Rogers and to come in and play Alexis Castle. All you want is for someone to come and for you to say, "Oh my God. This is it. This is who it is. This is perfect." And that was Molly Quinn. So yes, since Day One, she's been amazing. When she started, she was quite young, but now she's grown. It's weird. She only gets better than "amazing." It's quite interesting to see someone come to you who's so talented and who just keeps getting better.
 
 
HitFix: What do you think she brings out in you when you get to do scenes together?
 
NF: I find that the better the actor you work with, the easier it is to do your job, because you find that other people basically do your job for you. I don't have to spend a lot of time getting into character, trying to get inside Castle's mind and "What's it like to be Castle?" when I'm looking at Alexis Castle treating me like her dad. She's done all the hard work for me. All I've gotta do is remember my lines and she helps me with that too, by the way.
 
 
HitFix: Is she more professional on-set than you are sometimes?
 
NF: Well, here's the deal: I work every single day, so I've got a lot of lines to memorize and a lot of stuff to do. She comes in and I'll say "Let's run lines..." and I'll run lines with her and I'll call for a line and she'll know my lines. I'll say, "What's that line?" and she goes, "You say this..." It's hard to find someone who can memorize the entire scene. For you. And be able to coach you through.
 
 
HitFix: How has Penny Johnson's presence in the cast changed the energy on-set this season?
 
NF: You know what? It can't be an easy thing to walk into a cast -- and I know it's not, I've done it a couple times -- to walk into a cast, they're set, they're established, they've all been together for years, they have a groove, a certain way of doing things. It can't be easy to come in and settle in, but Penny is a great fit. Number One, she's amazing at her job. Number Two, she's amazing personally, she's really great to have around. So that's the best you can possibly hope for, someone who comes in and knows their stuff and knows how to do the job and elevates the material and is personally fantastic to be around.
 
 
HitFix: And her character brings up a lot of the implausibilities that you mentioned earlier, that this guy would be allowed to just run around the cops all the time. Do you like having that ridiculousness exposed a little and brought up?
 
NF: Absolutely. I love strife. You have someone like Castle who's very practiced at being around women. He's comfortable around women. He's surrounded by women constantly. He's got two wives, he's got a daughter, he's got a mother, he's got Beckett. He's always been around women, not a lot of male role models in this man's life. So when he wants to, he certainly can just charm a lady. It's a piece of cake, charming ladies. Penny, her character, will not be charmed. She will not be fooled. She's nobody's fool. You can tell that she's fought a battle to get where she is. She's worked hard and she won't have this idiot come in and just dance around like it's his personal playground. She won't have it and she will not be charmed. And it drives Castle crazy, because he wants to be liked.
 
 
HitFix: Obviously losing an actor of Ruben Santiago-Hudson's stature is one thing, but what are you going to miss the most about working with Ruben day-to-day?
 
NF: You know what? I find that it's a little bit different working with an actor who has a family. I find if someone is married or has kids, especially, I find their priorities to be fantastic. I find their sensibilities... I'm not married, nor do I have children, but I find I have very similar sensibilities to family men. And Ruben Santiago-Hudson is that kinda guy, his family is all-important to him. I like those kinds of priorities. So as much as I miss the character and as much as anybody might love the character of Roy Montgomery on "Castle," you have no idea of how amazing that man is personally and how much fun it is to have that guy around personally. And he's had a lot of history in this entertainment industry and he has some great stories and he's learned some amazing lessons and I'm only too eager to learn from somebody else.
 
 
HitFix: As sorta a last question: You've been in this character for a few seasons now. Give me a couple things that you still want to learn about Richard Castle.
 
NF: Well, as we touched on earlier, Castle doesn't really care about not having a dad, it doesn't impact him. There's no effect on him. He's never known his father. He doesn't know what he's missing. I'd like to know not only who is father is, but what kind of effect it's going to have on him, learning who his father is, what that's going to do to him. I want to know.
 
 
HitFix: And do you have an impression that that's a question the writers also care about?
 
NF: I do have that impression. 
 
 
HitFix: Is that coming up soon or nebulously?
 
NF: I'm told that we can look forward to it.
 
 
"Castle" returns to ABC on Monday, September 19 at 10 p.m.