There comes a time when all long-running procedurals must answer a simple question: How long should this show go on? One show definitely facing that question this fall is Castle.

The charming ABC drama is coming off its lowest-rated season, which, despite finally featuring the marriage of mystery writer Richard Castle (Nathan FIllion) and NYPD Detective Kate Beckett (Stana Katic), many fans found to be creatively uninspired. Making matters worse, the show's renewal was left in limbo while the cast's contract renegotiations went down the wire, forcing the show to craft a season finale that felt a lot like a "just-in-case" goodbye.

Everything you need to know about Castle's new season

But once all the actors' deals were in place, the show did receive an 11th-hour renewal, and over the summer two new showrunners -- Alexi Hawley and Terence Paul Winter, both veteran writers on the show -- were handed the keys to Castle. But the question remains: How much life is left in the show?

"We think there's a long life still in the show," Hawley tells TVGuide.com. "Part of what we're doing this season is trying to add a little bit of new energy to help pave the way for where it can go and expand it. We're very fortunate to be in an eighth season, but you also don't want to just keep doing the same thing. We've done 151 episodes. We've told a lot of stories. At the end of the day there is only a finite number of robberies and murders. For us it's really about the characters [and] trying to craft some fun new, fresh dynamics between our characters."

For the new bosses, that starts with shaking up the status quo and bringing in some fresh blood. This season, Beckett has been promoted to captain of the 12th Precinct. But when Beckett mysteriously goes missing in the premiere episode (Monday at 10/9c, ABC), Castle will find himself relying on the skills of Hayley Shipton (new series regular Toks Olagundoye), a former Scotland Yard police officer-turned-security specialist, to track down his missing bride. Castle quickly realizes that Hayley has her own way of doing things.

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"She's a strong sassy girl. She's got her own idea of what's right and wrong," Olagundoye says. "She's got a lot of integrity and lives within her own boundaries, which might be a little farther out than other people's boundaries."Naturally, Castle, Ryan (Seamus Dever) and Esposito (Jon Huertas) are a bit suspect of this new force, but that's just fine with Hayley. "She's from a rough background. She knows you have to prove yourself before you get trust," Olagundoye says. "I don't think she would understand anyone trusting her before they really know her. And I don't think she's really bothered either. She's incredibly capable. She's not concerned with what anybody else thinks."

It's that attitude and energy that Hayley brings to the show that the producers are hoping will blow up existing character dynamics. And that applies outside of the precinct as well, once Hayley takes Castle's daughter Alexis (Molly Quinn) under her wing. "What we really like is the idea of her as sort of a mentor figure to Alexis, who's now a 22-year-old woman," Hawley says, noting that Alexis crosses paths with Hayley while working for Castle at his P.I. agency. "We felt like it was a relationship the show didn't have and one that I think is very valuable to us. ... It felt like it was time to grow [Alexis] up in a fairly substantial way. She's a clever girl and she gets excited about the same kind of things that her dad does. So she's still finishing up college, but she's young and she's having fun."

But don't worry. The show's interest in Hayley does not extend to homewrecking. The producers insist the character was never meant to be a romantic threat. That said, Castle and Beckett's marriage will be tested, thanks to other changes this season. "It's a much different dynamic when your wife is your partner versus when your wife is your boss," Winter says. Adds Hawley: "Beckett becoming captain does form a little bit of a separation between her and Castle because she's not a detective solving cases. It does give us an opportunity to sort of widen their relationship a little bit, and get Castle running around and interacting in every episode with the 12th Precinct and sometimes against them. Again, it's adding a little bit of extra conflict."

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But Hawley says it's most important to have the conflict come out of character. As such, the two-part season opener brings back Senator William Bracken (Jack Coleman), the man responsible for the murder of Beckett's mother, which leads to a whole host of secrets between Castle and Beckett. "Relationships getting challenged is what makes relationships stronger, and at the end of the day, I think it's healthy for them and for the show to just poke at them a little bit," Hawley says. "What happens when a 16-year obsession suddenly ends? Can you just turn the page, or is there some sort of emotional PTSD that's going on? There's an opportunity to get a little bit deeper into these people... and sometimes things get a little messy. We don't want a one-dimensional relationship. As much as we love to see them happy and frolicking -- and it's not like we won't see them do that this season -- it's just not a hundred percent real to do that all the time."

Even so, the producers know that Castle and Beckett's romance is key to the show's appeal. "The reason the show was so successful off the bat was that spark between the two of them, and that spark was built out of a little bit of conflict," Hawley says. "It was built out of their sexual tension. So part of our desire this year is to try and figure out fun ways to add that tension maybe back into the show in a way... to service their love affair." Adds Winter: "We've had the honeymoon last year. Now it's about... what's the next evolution of their life together?"

How many evolutions does the show have left? Even though the first hour demonstrates significant reinvention, should fans look at this season as the beginning of the end? "Our goal going into this thing was to create 22 episodes that tell a complete story -- beginning, middle, and end -- with the hope that at the end of the season it just launches us into new storytelling for Season 9," Winter says. "Obviously we have no control of that. It's not really up to us. So, if this is the last season, our plan is to have a very compelling ending just like there was a compelling ending last season when there was a thought that it might have been the finale as well."

Castle premieres Monday at 10/9c on ABC. How much more of the show do you want?