Castle stars Nathan Fillion, Molly Quinn and Susan Sullivan, from left.

Dating back to at least Moonlighting, the conventional wisdom has been that TV shows based on a "will they or won't they?" dynamic tend to tank once those characters finally hook up.

The lead couple of ABC's Castle -- mystery novelist Richard Castle (Nathan Fillion) and homicide detective Kate Beckett (Stana Katic) -- have been firmly in the "they will" (and have) camp since the season four finale in 2012. It didn't seem to slow the show's momentum so much as satisfy the fans desperate to see the two together, and the characters are now engaged as of season six.



Two episodes into the sixth season, Castle stars and executive producers appeared at The Paley Center for Media in Beverly Hills on Monday to discuss the evolution of the crime dramedy, and taking the "un" out of "unresolved sexual tension."

"It was a challenge, yes, but it was a challenge we were really excited to face," Castle creator Andrew Marlowe told Spinoff Online on the Paley Center red carpet. "I'm somebody who believes that when you get into a relationship, the fun doesn't stop, and there are plenty of opportunities to grow a relationship. I think it's very easy to transition from, 'Will they or won't they?' into 'How will they?' when it happens, and see two people who are very different negotiate their lives together. So far, it's worked out, and hopefully we'll be able to continue that."

The coupling of Castle and Beckett hasn't been without its challenges, however. At the start of season six, Beckett relocated from New York City to Washington D.C. for a job in the FBI, creating some significant geographic distance between the two.

"We always want to keep the storytelling fresh, but we also always want to deliver the show that people know and love, and that's built around Castle and Beckett and their relationship," Marlowe said. "As we expand our storytelling, we know that what we don't want to lose is that core value, and that's really the challenge for us, but we've had a really good time tackling those issues."

This latest obstacle could stick around for a while, according to the show's creator.

"Trying to find a rhythm in relationship is something that we'll see them struggling with through the early part of the season," he said. "And when they do find a rhythm, other things are going to come up."

Katic said that she sees her character's move to DC -- where she's been paired with Castle newcomer Lisa Edelstein, known for her role as Cuddy on House -- as an intriguing change of venue for Beckett, despite the romantic complications.

"I actually enjoyed those changes," Katic told the crowd during the panel. "I thought it was really nice seeing her trying to fight to prove herself."



Beckett's departure affects more than just Castle, as it also provides an opportunity for her former colleagues at the NYPD, detectives Kevin Ryan (Seamus Dever) and Javier Esposito (Jon Huertas).

"I'm excited about the possibility of Ryan and Esposito really proving themselves as two fierce detectives to be reckoned with when it comes to solving the big cases," Huertas told Spinoff. "We have a really big scene coming up next week when we're put in harm's way, and have to battle our way out of it."

Castle and Beckett aren't the only couple on the show -- Castle's daughter Alexis, (Superman Unbound's Supergirl, Molly Quinn) now has a boyfriend named Pi, played by Myko Olivier.

"For her to be experiencing love so late in life, it's going to be difficult for her," Quinn told Spinoff. "Now that she feels so detached from her father, if she loses Pi, who does she have to fall back on? This is all she's got." In its sixth season, Castle continues to have success with mainstream network TV audiences -- the season premiere netted a reported 11.46 million viewers -- while also receiving the the type of passionate fan attention usually reserved for cult-favorite shows, like the short-lived Firefly, also starring Fillion. On Monday at the Paley Center, it was said that fans had waited in line since 2 a.m. that morning to ensure a good spot at the panel.

"It's really hard for us to fathom," Marlowe said. "I think at the end of the journey we'll be able to understand it better, but for now it's just great to be able to make TV shows, and it's great to have a great relationship with our fanbase. Everything else is really otherworldly to us."



Castle star Nathan Fillion.

Even though Susan Sullivan, who plays Castle's mother, Martha Rodgers, has been on TV for more than 40 years -- from Another World to Falcon Crest to Dharma & Greg -- she says the response from the Castle viewership has been a unique experience.

"In the past, I don't remember fans," Sullivan said to Spinoff. "I know Falcon Crest had fans, but I don't remember these kinds of events. We did an auction lunch as a fundraiser, and these three gals were all big Castle fans, and they met at a Castle event, and have become best friends. I thought, 'Oh my god. That's what it's about.' The family of fans."

The popularity of Castle led to its crossover into the comic book world, with a series of graphic novels from Marvel Comics -- three so far -- from creators including Brian Michael Bendis, Kelly Sue DeConnick, Peter David and Lan Medina.

"We didn't start from a comic book, like a lot of TV shows, but we created one off the show," Marlowe said. "That was easy, because you're working with folks at the top of the game. That was a lot of fun."

All involved at the Castle event at Paley Center were quick to express their gratitude -- both for the show's six-season run, and its ardent support from fans.

"I'm very happy being employed," Fillion said. "This is the job I've chosen, and it's not a success-oriented career. We have won the lottery."