Disclaimer: I don't own Castle. I don't even own the idea. This is a fill taken from the prompt as part of the winter kink meme, run by airbefore. This got a little bit wordy a little too quickly. Sorry, OP, I hope you like it anyway.

She's never thought of herself as straight, when she thinks about it.

She's just never considered herself not straight.

Kate Beckett has been working with Ricki Castle for all of three months and already the dreams that have her waking in a confused haze late at night have grown far more vivid than they'd originally begun. Dreams of skin so soft to touch, swells and curves that are new and unfamiliar but feel right beneath her palms. Dreams of those blue eyes and the way they light up with a crazy new theory and that stupid, self-satisfied grin of hers and oh, what that grin would look like as she perches between her thighs and Beckett twines her hands through her hair and –

Kate blushes, eyes darting around the precinct to check nobody's been watching her as she crosses her legs and desperately tries to keep her mind from Castle. It's been swelling inside of her slowly, a burn so patient, like nothing she's ever known. The worst part is that she can't even stand the woman, most of the time. Or, at least, she likes to pretend she doesn't.

"Hey."

She looks up to see Ricki- Castle, rush around the corner of the bullpen, coffees in hand. It shouldn't make her heart swell. It shouldn't. But even on their second case together – when Castle had brought her the correct coffee order without asking and made a stupid joke – it had caused that stupid flutter of her heart.

"Hey," she says, accepting the coffee gratefully. She doesn't know when she'd stopped making her own and had simply began relying on her shadow.

Castle teeters on the edge of her seat as she watches her, so she rolls her eyes.

"Spit it out, Castle."

"Just listen for a sec, before you get all Castle, that's insane on me," Castle says, pouting.

Kate fights with all her power to drag her eyes from Castle's lips to her eyes before she can notice. It's not quite quick enough, she thinks, as she notices that quirk of the lips Castle gets sometimes. Damn. You tell her a girl that she'd have no idea and suddenly she wants to base character on you.

"Fine. Tell your tale, Castle."

"It's not a tale, it's a perfectly plausible – "

"Castle. Spit it out."

Ricki's eyes glitter delightedly as she spins her tale involving an illicit lesbian love triangle, the mafia, three tonnes of cocaine and a religious sacrifice. Sometimes, Beckett thinks that if Castle hadn't begun writing mystery novels, they'd have a highly intelligent – although completely insane – murderer on their hands.

"That's…"

"Brilliant?"

"No."

"Inspiring?"

"No. Crazy," Beckett says, sipping her coffee again. "Now until you can think of a realistic, plausible, reasonable explanation, please don't open your mouth again. It's only 8am."

"I know," Castle laments dramatically. "You wake me up so early."

"I didn't tell you to come in at this time, Castle. That was your choice."

Castle lets that smug grin of hers spring loose on her lips. "Oh, you keep me up at all hours, detective."

Kate scowls at her, but has nothing else to say.

They do catch the killer, eventually. It doesn't involve any of the creative ingredients that had formed Castle's earlier explanation, much to her disappointment. It does, however, lead back to an unresolved case from the 1980's, so that's enough to fill her childish excitement once they worm a confession from their killer.

"I told you this case was gonna be interesting," Castle says, bouncing up to Kate's desk, and Beckett absolutely does not stare at the button that strains against Ricki's chest as she does. "Didn't I tell you?"

"Yes, Castle," Beckett sighs. "I heard you the first ten times."

"Aw c'mon, Beckett, we got the guy. That should put a smile on your face."

"What would put a smile on my face would be you finishing your book and leaving me alone," she retorts, looking up from her paperwork to see the minute flicker of something sadder behind those blue eyes.

"You don't mean that," Castle says. "I know you don't."

"You do, do you?" Beckett challenges.

"I do," Castle says simply, and then she's moving.

Kate feels hands close around her arms and her face flushes, being touched by those same hands she's now grown accustomed to dreaming about as her own creep between her legs late at night. Castle simply yanks her out of her chair, tosses Beckett's coat at her, and announces that they're going for a drink in order to put a smile on her face.

"I'm not going out for a drink with you," Beckett argues.

"Would it be more comfortable for you if I invited Lanie along? We could have an all girl's night. Ooh. I do love those."

Beckett rolls her eyes. "Is there anything you can't make into an innuendo?"

"Is that a challenge?"

She doesn't even realize she's agreed to go out for drinks until Lanie's meeting them at her cruiser.

Lanie leaves them when Beckett considers herself mildly tipsy, alcohol warming her lungs and making her feel a little looser than usual. The medical examiner tosses her one of those looks that remind her of their recent girls nights, when Lanie says things like we all know how she looks at you that have Beckett's mind conjuring up images that are a little less than decent for public. Beckett pretends not to notice.

Castle leans her arms on the table, glancing at Beckett thoughtfully before speaking. "I used to come here all the time, when I was younger."

"Well, it was your idea to come here," Beckett says dryly.

"The Old Haunt. So many good memories," Castle sighs dramatically. "I should bring Alexis here."

"You want to bring your daughter to a bar?"

"So she can see where I wrote my first book!" Castle splutters indignantly. "Jeez, Beckett, don't make everything sound so dirty. That's my job."

"Sorry," Beckett apologizes quickly, though the amusement seems to have crept back into Castle's eyes regardless.

Castle cocks her head to one side, dark hair falling around her shoulders in choppy waves as she studies Kate curiously, warmly. Kate knows that look. Has been on the receiving end of it from many men who approach her in bars, even a few women. But never has she felt such a stirring in the pit of her stomach in response before.

Maybe she is not straight.

Maybe she should stop – stopping.

"I make you nervous?"

It's not so much a question, as such, but Kate shakes her head anyway.

"No. Not that."

Castle ignores her, smiling. "It's because I'm so hot, right?"

Ricki laughs at her own joke to break the sudden silence, and Kate feels her heart pounding ridiculously quickly in her chest. Maybe she could – maybe she could just try. The woman is gorgeous, outrageously so, all devastatingly charming eyes and smiles. And she makes her laugh, which nobody else really can nowadays. Despite all the innuendo, too, there's a wonderful mother hidden deep inside, and a doting daughter, and soft eyes and words when Beckett had told her about her mother.

And she knows without a doubt that she'd be really, really good in bed.

Before she can give herself the chance to regret her decision, Kate darts forwards, captures Castle's smiling lips with her own.

Oh – It's. Not uncomfortable.

A little different, maybe. But nice. Oh. Definitely nice.

Castle's lips are soft against hers, still for a moment before a hand reaches up to curl at the back of Beckett's neck, tugs her closer. She follows willingly, until their thighs are aligned, chests pressing together and yes, yes, that feels good. So – so good. Castle really knows how to kiss.

She pulls away with a loud smack of lips, fingers shaking and pulse in her ears as she asks, "You wanna come back to my place?"

The buttons of her shirt are scattered across her hallway floor the moment they step inside her apartment. Castle's fingers burn her skin, molten lava against her waist before their lips separate and Castle's mapping a path along her jaw. Kate tilts her head back, grasps Castle's own shirt desperately as arousal overwhelms her, makes her knees weak.

"Bed," Castle mutters against her skin. "Now, Beckett."

Beckett nods in a daze, so unused to the feminine scent surrounding her as Castle keeps herself pressed against Beckett's back as she leads them to the bedroom. It's still good. She can do this. No backing out now.

She really, really wants to do this.

Castle presses her down onto the bed, hands fiddling behind her back and undoing the clasp of Beckett's bra expertly. Without giving her time to think, Castle's hands have torn the bra from her body and toss it elsewhere in the room, one hand cupping her left breast as her mouth moves down to the other, lips closing around its swollen peak.

Beckett gasps, fingers gripping the sheets of her bed as her eyes close in delight. Castle's tongue and lips and fingers are doing something wonderful to her in ways she couldn't have anticipated and she hasn't even gotten her pants off yet.

Kate curls a leg around Castle's waist, distracted by her ministrations on her chest until a jean-clad thigh falls between her own, pressing against her crotch. Beckett sighs contently as her hips undulate against it, the friction not quite enough yet but oh, she can feel herself growing wetter with every roll and swirl of her hips.

Castle smirks, lips drawing away from her chest and heading back up to her lips.

"So impatient," she mutters before moving away.

Kate whimpers at the sudden loss, eyes opening to see Ricki perched between her legs as they fall open for her. She grins, and Kate barely as the time to scowl before Ricki's reaching for her pant buttons, dragging the zipper down far more slowly than necessary. Beckett bites her lips as she watches Castle watching her, sending all sorts of warmth zipping through her. Castle drags her pants down her legs, pressing wet kisses against the inside of her thigh as she trails back up, Kate writhing and panting beneath her.

"Tell me what you like, Beckett," she says, avoiding her aching center and pressing a kiss against her hip. "Show me."

Kate's heart freezes where it lurks behind her ribs. Her mouth opens, but nothing comes out, no sounds can be made. She doesn't – She knows what her own body likes, what she responds to. Will it be the same with a woman? Does it matter?

The moment drags out for far too long, and Castle's sitting up, the previous arousal quickly receding.

"Are you – Crap, Beckett, have you ever done this before?"

"I…"

God. What can she say? She should've said something earlier. It was unfair on Castle not to say anything.

"Are you straight?" Castle questions her, eyes as wide as saucers. "What the Hell, Beckett?"

"Yes," Beckett answers without thinking. But then: "No, I don't – I'm not –"

All of that playfulness she's become so accustomed to seeing has been distinguished from Castle's eyes. Castle's shaking her head, bitter tears lurking in her eyes.

No. No, this isn't want she'd wanted to happen – She'd wanted – She still wants –

Beckett rises quickly, grabbing Castle roughly and kissing her with everything that she has. Castle kisses back fiercely, all hot tongue and nipping teeth. She whimpers into the kiss, breaking away as she clutches desperately at Castle's shoulders.

"I don't care," Beckett tells her. "I don't care about what I am. I want you. I want you so much, Castle."

Castle pushes her away, rolling her eyes. "I've heard it all before, Beckett. Straight girls are all the same."

"Like Hell you get to decide that," Beckett says. "What do you want me to say? I don't know what I am, and right now, I don't really care. God, you're all I can think about, all day. All night."

A glimpse of the familiar Castle she knows lurks behind the sadness of those blue eyes, if only for a moment.

Beckett tears her panties from her legs, grabs Castle's wrist and cups her palm against her centre. She shudders at the feel of the long, thin fingers against her, eyes hooded with lust.

"Can you feel that? This is how much I want you," she tells Castle, watching the smug exterior return, but she's too far gone to care about how much she's filling her ego right now. "So show me, Castle. Touch me."

Castle rips her own blouse from her skin, revealing a lacy black bra beneath. Beckett's eyes drop to her full, heaving chest immediately, a flush creeping up her neck as she stares, finds herself licking her lips in anticipation.

"Here," Ricki says, unclasping her own bra to reveal her bare breasts. "Like this."

Castle guides Beckett's hands to her breasts, and Beckett finds it all happening on instinct, the way she rolls the pert nipples between her fingers and watches as Ricki's eyes roll back into her head, her breath stuttering. Slowly, she pushes Castle onto her back, straddling her as she lowers her mouth to one firm breast. Ricki writhes beneath her, and Beckett's own instincts are going into overdrive, hips grinding roughly into Castle's jean clad own.

Castle lets out a low moan when Beckett nips at the underside of one breast, so she does it to the other just to get the same reaction. It shoots warmth straight to her core and shaking hands are ghosting over feminine curves that make her heart race, and then she fumbles to rid Castle of her jeans and panties by tugging them down her legs.

She hesitates, can feel Castle watching her, as she stares at the sight before her. This is really, really not where she thought she'd end up when she first met the womanizing millionaire.

"Hey."

Beckett lifts her gaze up to meet blue ones.

"You okay?"

So tender, so unlike her – she could get used to that.

"I'm okay," she assures Castle.

It's new, of course, when her fingers slide between Castle's wet folds. She's a little clumsy, uncertain, as she draws circles over her clit, but she must be doing something right because Castle's hips lift from the mattress, moans spilling from her lips. She wants to hear that sound again, get that same reaction that makes her ache so much, and so she slowly slips one finger inside and adjusts to the feeling of muscles fluttering around her.

"Beckett," Castle groans when she begins thrusting. "Kate."

Kate grins, slipping two fingers inside this time before she leans forwards, pressing their breasts together and kisses her sloppily, lazily. "I like it when you say my name."

"Yeah?" Ricki pants.

"I love the feel of you around my fingers," Kate tells her brazenly, resulting in Castle's hips to thrust shallowly against her fingers. "So tight and warm. For me. You like that? What I'm doing to you?"

Castle nods, swallowing loudly. "God, yes. You've no idea… God, Kate."

Kate curls her fingers and presses her thumb against her clit at the same time, and then Ricki's curling a hand around the back of her neck tightly, mouth open on a soundless cry as her muscles squeeze and contract erratically, hips jerking wildly as wetness fills Kate's palm. Kate watches in fascination as the woman below her shatters apart, dragging it out as long as she can before Castle's body goes limp.

She pulls her fingers out slowly, wiping their sticky wetness against the inside of Ricki's thigh. She waits patiently, albeit nervously, until Castle comes back to herself, eyes opening as she grins.

"You know, you're amazing at that. For your first time."

"Yeah?"

"Yeah. But now I'm gonna show you mind-blowing."

Kate smirks playfully. "Prove it."

She's on her back before she can think, soft and long fingers sliding through her own folds and oh-

It's wonderful, as Castle's tongue begins probing her mouth with at the same rate the first finger thrusts into her. Kate reaches out and grips her soft waist desperately, hips rocking, nails digging and marring the skin there.

"Ricki," she pants, "God, Castle. So good."

Castle smirks. "I know."

Kate's eyes fall closed and she feels Ricki move away, but a second finger has joined the first so she cannot spare the moment to think, can only fist her hands in the sheet and feel-

Until suddenly, the flat of Ricki's tongue is pressing against her clit, and everything inside her coils at once.

"Holy – Crap – " She grits out, and then the moans that filter to her ears do not sound like hers at all, but some distant part of her knows that they must be.

Ricki keeps thrusting and scissoring her fingers inside of her and laps at Beckett's wetness. And, God, she opens her eyes to see Ricki down there and her hips are grinding roughly into her palm and her hands are sliding into Ricki's silkly hair to somehow gain more pleasure than she's already getting, hips bucking wildly, and God, this is everything she's fantasised about – no, it's more. So much more.

"Ricki," Kate pants. "I can't – "

There's no room left for coherent thought when Ricki's fingers curl and find just the right spot as her tongue draws little circles on her clit.

Kate falls apart with Ricki's name on her lips, not for the first time – but for the first time her fingers are in her hair and those fingers aren't hers and everything inside of her is melting. Surely, this is too much, too much. She's barely even given time to catch her breath before Ricki's moving again and she shatters apart all over again, loudly and unashamed.

When she comes back to herself, Ricki is stretched out beside her, smiling smugly.

Kate grins, reaching out to stroke a hand against the soft dip of her hip. "I can't believe I've been missing out on that all this time. I had no idea."

"I know. I'm amazing. Tell me again."

She rolls her eyes. "Alright, stud. Cool the ego for a minute."

Ricki laughs, delightful and gorgeous and flushed and yeah, Kate really doesn't give a damn about sexuality anymore.

"You know that you're more than a conquest, right?" Ricki asks, sobering for a moment.

Beckett swallows roughly. Damn this woman. One moment the class clown, the next tender eyes and warm touch.

"I know," she murmurs quietly.

Ricki grins. "Does this mean I can tell Ryan and Esposito you're my girlfriend?"

"No!"

"Lanie?"

"No, Castle."

"Mont – "

"What did I just say?"

Ricki sighs dramatically, throwing an arm across her eyes. "I guess I'll just continue to put up with the awkward come-on's from Espo."

Kate giggles. "Don't worry, Castle. He'll definitely understand the definition of gay eventually."

He does. When he points out the hickey on her neck the next day and the first thing she does is glare at Ricki.

The End.