Nathan Fillion and Stana Katic, <i>Castle</i> Nathan Fillion and Stana Katic, Castle

In the opening moments of Castle's Season 3 premiere, crime-solving partners and star-crossed lovers Castle and Beckett have their guns pointed at one another.

We knew there'd be some tension after Castle (Nathan Fillion) left Beckett (Stana Katic) to run off to the Hamptons with his ex-wife (Monet Mazur) at the end of last season. But this?

While everything may not be as dire as it first seems, there is definitely some bad blood to be worked out.

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"I knew after the way we ended last season, we couldn't just have Castle walk back into the precinct and say, 'Hey, I'm back,'" creator/executive producer Andrew Marlowe

tells of the premiere, which features Castle as a murder suspect. "We get to see Castle and Beckett on opposite sides. I knew the notion of Beckett being able to put Castle in the interrogation room on the other side of the table and ask a bunch of questions — the subtext of which is, 'Where have you been? Why didn't you call?' — was going to be a lot of fun for viewers."Don't look for the duo to stay at odds for long, but don't expect a magical hookup either."I don't think they're back to square one," Katic says. "They have so much history. ... There's nothing that can untie that kind of a bond between those two characters. Once they get past this hurdle, then they'll be diving into another level of a friendly relationship. But he comes back in a relationship, so they're not going to be making love anytime soon."Katic says Beckett will continue to maintain her composure around Castle. "I don't think she'll do the spite thing; she's not that girl," Katic says. "She has a tremendous amount of integrity. In the realm of love, she really has a huge heart. She might have been in a relationship over the summer."

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Indeed, a new love interest for Beckett, played by Charmed's Victor Webster, will be introduced in Episode 4. But Marlowe maintains that these continued speed bumps for Castle and Beckett will only make it sweeter when they finally do connect."If you don't create obstacles, the flirtation will lead to something much sooner than the audience wants," Marlowe says. "Part of our metaphor in the early stretch of the season is that these two characters, who many feel belong together, 'married' the wrong people. So, we root for them to wake up and find each other again."Meanwhile, Castle will deal with a loss in his family as well as the continued struggles of parenting a teenage girl. Those struggles kick into overdrive when Alexis (Molly Quinn) starts dating, Fillion says.

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"She's 16 now, and that's the time the hormones start kicking in and telling us it's time to rebel, it's time to push the envelope, it's time to break the rules," Fillion says. "We'll see that teenage angst, or at least Alexis' version of that angst, because she's a pretty well-balanced kid."

And whatever embers of office romance still burn come November sweeps will momentarily be doused as Castle and Becket focus on a new foe: a serial killer who murders in threes.

"We have a villain for Castle and Beckett who can be in the wind and continue to complicate their lives and investigations," new executive producer David Amman says. "He's pretty dark, but not to the point that it's a violation of the bounds of the show. When he's in the interrogation room with Castle and Beckett, he's a force to be reckoned with — inside that room and out."

Still, Katic thinks now might be the perfect time for Castle and Beckett to give a relationship a try. "I think they make sense for each other," she says. "I'm the only one on the entire team who's like, 'So what if they get together?' ... Maybe I'm overly romantic thinking that when people get together, they should still have that spice and fire. They should still have the same swordplay."

Castle premieres Monday at 10/9c on ABC.

(Additional reporting by Natalie Abrams)