A/N: This is a variation of a prompt I saw on Tumblr and I intended on following the prompt, but the story sometimes goes its own way.

The knock on Kate's door startles her and makes the hair on her neck stand straight. Grabbing the gun that lays beside her on her couch, she hesitantly stalks toward the entrance. Taking a quick peek through the peephole she spots the perfectly coiffed hair and piercing blue eyes of her partner. She swings the door open and stares at him with uncertainty.

"Can I come in?"

"Yeah," she says simply as she opens the door further to allow him entry.

Castle walks into her apartment with purpose as he reveals the recent developments of her mother's case. "So, we went over all of Raglan and McCallister's old arrest records, and you were right," Castle pauses briefly as Kate steps toward him, "there was a third cop that was with them on a lot of those arrests. But, then someone went back into those reports and removed their name. So, Ryan and Esposito are right now looking into who was running the records room back then."

Kate sighs, "Castle, you couldn't've just called me and told me this over the phone?"

"Well, yeah, I…I thought that…" Castle hesitates, not sure how he should broach the topic.

Kate catches on to his uncertainty and goads, "Castle, if you got something to say, just please say it."

"Beckett, everyone associated with this case is dead. Everyone," he emphasizes. "First your mom and her colleagues, then Raglan, then McCallister. You know they're coming for you next."

Kate shrugs and walks past Castle to put down her gun. "Captain Montgomery's got a protective detail on me. Wasn't that hard to spot."

"That's not going to be enough to stop Lockwood; you know that. Think about what they're up against. Professional killers? I-I've been working with you for three years; you know me. I'm the guy who says we can move that rubber tree plant. But you know what, Beckett? I don't think we're going to win this."

"Castle, they killed my mother. What do you want me to do here?" Kate asked, appalled at what her partner was suggesting.

"Walk away," he says concisely. "They're going to kill you, Kate. And if you don't care about that, at least think about how that's going to affect the people that love you. You really want to put your dad through that? And what about Josh?"

Kate jumps on his words, needing a direct answer to what their partnership means, "And what about you, Rick?"

"What about me, Kate? We've known each other for three years and in that time I have come to know you as the most difficult, maddening, challenging person I have ever met and yet I am by your side nearly every day." Castle takes a deep breath as Kate moves her weight from one leg to the other and purses her lips in an attempt to hide emotion, "I've come to the realization that I don't follow you around because I have a morbid curiosity with murder or because I feel a sense of purpose with helping, I do it because I've fallen head-over-heels, shout-it-from-every-rooftop in love with you and the thought of being away from you for even a day makes me feel like I'm barely able to breathe. It isn't until I see you again that the burning ache in my chest eases and I no longer feel like I'm drowning." Castle stops again, his eyes wide and worried as he stares at the woman before him.

Kate's bottom lip quivers and she crushes it into stillness with her teeth. "Rick," she whispers.

"Kate, I love you and I want you to know that if something ever happened to you, I don't think I would survive. Every breath would be a struggle and I'd be living only in the sense that oxygen enters my lungs and leaves again. I wouldn't be living with a purpose because you wouldn't be there." Castle chokes back a sob.

"I don't know who I am without this case," Kate admits on a breath as her eyes fall to the floor.

"Let me help. I know you hide in your mother's murder like you hide in these nowhere relationships with men you don't love, but Kate I love you and I truly believe you have similar feelings for me but you're afraid. You deserve to be happy and even if you don't find happiness with me, I just want you to be living a life where you do."

Kate meets his eyes again with tears slipping down her cheeks. In a matter of moments Kate spans the short distance between them and grasps his face between her palms before smearing her lips against his. She slowly moves her hands to his neck as Castle recovers from the shock and wraps his arms around Kate's body. She deepens the kiss with urgency and circles her tongue around his. Just like their undercover kiss, Kate can't hold back the hum of pleasure as it escapes from her throat. The warmth of their arousal flushes their cheeks and pools in their bellies. Kate doesn't want to ever stop, but she feels the disappointing separation of their lips as Castle attempts to pull away.

"Kate," he struggles to speak, "we can't do this. I want to keep doing it but we can't. I don't want infidelity hanging over our heads."

"I just want you, Castle. I need you," she pleads before trying to kiss him again.

Castle holds her back. "There's nothing I want more than to kiss you, but what about Josh?" his brow furrows at having to mention her boyfriend.

"I broke up with him when we got back from L.A. I finally realized that I couldn't fight my feelings for you any longer and I didn't want to anymore," she give him a hesitant smile. "I love you, Rick."

Castle beams with delight before crashing his lips with hers again.

Briefly breaking apart, Kate says, "I want and need to put my mom's case away for now and I want you to help me. I want to be happy. I want to live my life. I want you." Kate's eyes shimmer with joy and truth and Castle's smile is full of adoration as he sees the conviction in her gaze.

"I'm able to breathe again," Castle states with a smirk as their lips meet for the third time that night.

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