Stana Katic

For the first time on Castle, Beckett will lose control.

As a sniper rampages through New York, Beckett (Stana Katic) will be faced with memories of being in the cross hairs of a sniper and taking a bullet to the chest in the Season 3 finale. "It's the first time that she is not on top of her game," Katic tells TVGuide.com of Beckett's reaction to the new case. "It's the first time she's in a space of pure fear, and it's unusual for her and she doesn't know how to handle it."

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Not used to weakness, Beckett will attempt to push her PTSD aside in hopes of willing herself back to normal. "For a character who's so used to being in control of a situation, it's like, 'OK, I don't have time for this. What do I need to do to get past this and get back on the case?' She is so used to being at the forefront of any investigation and is New York's superhero, basically. There's no time for weakness, especially now. She has to work through this and it's a tough one."

Castle (Nathan Fillion), who's usually quick with a joke to provide comfort, will be at a loss at how to help Beckett get through her fear that she could end up getting shot again. "This is the first time that Castle is completely immobilized and he cannot help her," she says. "The whole group sees that something is crazy-wrong with her, and they don't have the tools to help her through it. It's totally uncharted territory for her. The only person who does know how to help is Esposito [Jon Huertas]."

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To come out of this case physically and emotionally intact, Beckett will be forced to confront one of the basic notions that always has driven her. "She has been defining herself by her mom's murder, and she realizes that she doesn't want to define herself by that, anymore," Katic says. "It's caused her to make certain decisions. She became a cop because of it, and she's unable to invest in a real relationship because of it.

"She's not willing to compromise living life anymore," she continues. "This case brings that fear of losing life to the forefront, something she's been able to tuck away since the shooting, and now she can't anymore because it's so close to home and so close to her own experience. She looks at a dead body at one point, and that dead body is basically almost a mirror image of who she is and who she could've been if she didn't survive the sniper shooting."

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Coming to terms with her own experience is the first step in what could be a relationship between Castle and Beckett. "Beckett decides to choose that she doesn't want to be defined the unresolved murder case anymore. She wants to engage in the gift that is her life and engage in a gift like a relationship with Castle. That's not going to happen overnight, but that's a new direction for her now. It's a really sweet evolution to the character, to the story and to the love story. She comes one huge step closer to getting into that relationship with Castle."

Check out a sneak peek of Monday's Castle, airing 10/9c on ABC.