Author's Note: I wasn't quite happy with the chapter I was planning to post, so I'll work on it a bit more before sharing it with you guys. For now, let's assume it's Castle's turn again.

Warning: Rated M.

Fantasy Fridays
Chapter Four: Work it Out

The elevator doors close on Esposito and Ryan's smirking faces. The bullpen is dim. It's a quiet night for murder, but a few cops mill around their desks, filing papers or typing in the blue light of their computer screens.

"Yours or mine, Castle?" Kate asks, pulling her coat off the back of her chair.

Castle takes it from her and she turns, waiting for him to help her into it like he does every day. It's the only time she lets him get away with a bit of touching at the precinct. She secretly loves the way he pulls her hair out from under her collar, fingers lingering at the back of her neck under the cover of her curls. If he did that any earlier in the day, she'd get nothing done, but she allows it when they're on their way out the door.

She waits, but the coat doesn't come. She turns to face him, a question on her lips, but he speaks first.

"I thought you might want to get in a workout before we went home. I brought these, in case you didn't have any clean clothes here." Castle produces a small canvas bag from beneath his chair. She's been wondering about it all day, but hadn't had a chance to ask him what was inside.

He hands it to her and she fishes out her tightest black yoga pants and a strappy bright pink sports bra that she's never seen before.

"Usually I wear more than just a bra when I work out, Castle, but I think I have a shirt back there. You sure you don't want to go home? I mean, it is the end of the week and all…" she leans in and drops her voice. "So it's your turn."

"Believe me, I am not ever going to forget what day of the week it is. And this," he smiles, glancing down at the workout clothes, "is my turn."

Oh.

Kate does a sweep of the floor. Just LT and two other fairly new homicide detectives. LT leaves at the same time every day, so he'll be gone in about fifteen minutes. The other two … oh, what the hell. There's a lock on the hallway door that leads to the gym. And she did promise him she'd try.

"Okay, Castle. Let's go. You gonna hold my punching bag?"

"That's the idea," he leers, like it's some brilliant double entendre, and she doesn't even know how that makes sense. She laughs anyway and leads the way to the locker room.

They check that the gym's empty before splitting up into the changing rooms. Something funny happens to Kate's heart rate as she unbuttons her dress shirt, not bothering to take cover behind her locker door. She stands naked in the humidity before deciding she doesn't need underwear for this particular workout session. She slides her yoga pants on.

She takes the sports bra out of the bag. She's a bit of a nut for sexy workout clothes, but doesn't own as many as she'd like. She'll have to remember to thank Castle for this one. She navigates her way through the asymmetrical straps, poking her head out the wrong way before getting it right. It looks amazing on. Deciding to skip the t-shirt after all, she bends over and adjusts her breasts to maximize cleavage. She pulls her hair into a high ponytail. He's just going to love this.

When she enters the gym, Castle's standing with his back to her, rolling a medicine ball around with his foot. He's in navy blue basketball shorts and a matching (scrumptiously tight) UnderArmor shirt. Not for the first time, she's struck by how much muscle he has for someone who hardly ever works out. If she doesn't run for a week, her calves soften, but his are rock hard and defined even after months of inactivity. And those shoulders, damn. He's definitely not hard to look at.

When he turns around, the unsure boy in him disappears, replaced by the look she loves best on him. The look that says 'I'm going to take what I want from you without asking first.'

"Hold this, Castle," she says, moving to the black punching bag that hangs from the ceiling.

Fifteen minutes later, she's sweating, strands of hair are escaping her ponytail, and her knuckles ache under the protection she's wearing. They're both worked up. Only so much longer they can last.

"How bout some wrestling?" He asks darkly.

She laughs. This won't take long.

Sure enough, she pins him in seconds, one of his legs pressed between them, knee to opposite shoulder.

"Damn," he exhales. "I'm gonna feel that in the morning." She rolls off him as he gingerly massages his hamstring.

"Sorry, Castle. You should know what to expect by - oof -"

Suddenly, somehow, she's under him, his heavy, warm body pinning her to the floor. Shit. She did not see that coming.

"You were saying?" he growls. There's a smug little smile on his face, but another sweeter one beneath it that tells her he knows exactly how much she likes being taken by surprise. She'll have to remember to ask him where he learned that move later. Probably doing research for Derrick Storm. It reminds her of the time he came to find her in the shooting range and shot the grin right off her face. He's incredibly annoying. And incredibly sexy.

He grinds his hips into hers, pressing himself against her core. Earlier, when she was working the heavy bag, she'd noticed exactly when he began reacting to her, the loose fabric of the basketball shorts clinging to him as he grew. She'd always been a fan of, to put it delicately, certain parts of men, but this - him … God, nothing compared.

Castle lets his entire weight fall onto her as he reaches for her wrists and brings them above her head. He teases the fingertips of his free hand under the soft waist of her yoga pants, and then his control snaps. It's rough and crass when he shoves his hand down the front to curve his palm over her.

"Fuck, Beckett." He's discovered she's going commando, then. "This is so much better than I imagined it. And you're much, much wetter."

She can't help it, she has to know.

"When? Exactly - " Her words struggle to come out between pants as his palm digs into her clit. "When did you imagine it?

"That time we had to pull you from a workout to update you on a case. You were so sweaty, but I didn't mind."

That was years ago. Years.

"What did you imagine? In your fantasy, were you here too?" Unsure of what to do with her hands, they land on his ass, squeezing and pulling him closer to her.

"Mmm." His affirmative vibrates into her neck and she shivers as his stubble rakes over her.

"In my version, I cornered you in the locker room. Did unspeakable things to you up against the wall in the shower."

Kate winds her leg around his and flips them over smoothly, then she's gone, leaving Castle in a dazed slump on his back.

He cranes his neck up to catch a glimpse of her disappearing into the locker room.

She doesn't have to say it out loud this time.

You coming Castle?

Castle pushes the door open and hears the weak pattering of the shower, feels the humidity starting to gather. The women's locker room is a lot cleaner than the mens' and smells like plain, cheap soap instead of stale socks. He stalks slowly down the line of rusting turquoise lockers, pausing when he sees the yoga pants and the pink bra in a heap on the bench near Kate's open locker.

He draws in a breath. Three years ago, she would have absolutely murdered him for following her into the locker room, and now she expects him to, leaving a trail of clothes that flood his imagination with what he's about to see.

Holy fuck, I really am Kate Beckett's boyfriend. He'd thought he hit the jackpot when his books climbed the charts, giving him the kind of money and fame most people can't fathom. He didn't have any right to be so lucky two times in one life, and being allowed to love Kate is like winning the lottery all over again.

And then he rounds the corner and sees her and all of his blood rushes south. If he had a shovel he'd use it to scoop his jaw off the floor. Kate's standing under the spray, the flimsy cloth curtain left open to give him a full view of her magnificent body. He can't decide where to look, her outstandingly pert breasts, the long shining lines of her legs, or the apex of her thighs where she's got one hand pressed against herself, two fingers unaccounted for, palm grinding slowly, eyes locked on his, challenging.

"Getting started without me?"

She shrugs. "You were taking a long time."

Castle quickly strips off his basketball shorts and top and joins Kate under the water. He crowds in on her, keeping just a centimeter between their bodies, letting his heat taunt her. Her knuckles brush against his thigh, and he grabs her wrist, drawing her away from herself. He wants to take over, wants to be the one giving her pleasure. He drops his lips to her ear.

"You know what I was thinking out there?"

"Mmm, what?" she sighs, body loosening as he nudges her back against the tiles.

"About how lucky I am to be the one that gets to do … this." His fingers delve into her, thicker and more insistent than her own. She gasps, jolting hard and grabbing for his shoulders.

He's not gentle, not with his fingers pumping inside her, pulling incessantly against the spot that makes her writhe, and not with his mouth when he starts in on her neck, setting her on fire. It's too much, this voracious attack, heightened by the absolute filthiness of being in the precinct locker room, where she has so many mundane memories. Never did she think she'd be having sex in this shower. She knows they locked the hall door, but she can't help feeling a little on edge, a little excited that someone might catch them, her body naked and slammed up against the wall, her civilian partner's fingers working high inside her. It's just so inappropriate and completely against regulations and so fucking hot. She closes her eyes against the perfect torment.

She's about to shatter, and shatter hard. Castle scrapes his jaw just under her ear and sucks her earlobe into his mouth. He thrusts his words into her ear in rhythm to the movements of his hand.

"I'm so lucky to be the one that gets to. Make. You. Come."

And he does.

He doesn't slow down, leaving her empty for only a fraction of a second before purring into her ear: "But most of all I was thinking about how lucky I am to be the one that gets to fuck you."

And then he's pushing into her heat, impaling her on his unbelievably hard body, catching the tail end of her orgasm, feeling her muscles collapse around him. She cries out, a long string of obscenities and more than a few repetitions of his name, and then she's lifting her legs and taking it like a champ as he starts pounding into her. He always did admire her recovery time. It doesn't take long to get her close to the edge again.

She claws at his back, grating out, "Harder, Castle. I'm about to come again. Harder."

He's not too far behind himself when the water suddenly turns ice cold.

His reflexes are admirably fast. Castle snatches her off the wall, reaches behind her to turn off the water, and steps back holding her under her thighs, still buried deep inside her.

Castle looks around, wild with panic because he just needs to keep moving, keep chasing this bliss with her.

"Shit, Castle, we can't stop now," she whispers, apparently just as desperate as him.

"Oh, trust me, I have no intention of stopping. Do you think that sink will support your weight?"

Kate scans the room hazily. "I wouldn't bet on it. But I could just…" She slides down his body and grabs the battered metal chair the women use to hang their towels on and positions it in front of the full length mirror screwed to the opposite wall.

Castle's mouth goes dry when she bends over, leaning her forearms on the arms of the chair, grinning at him in the mirror. He's not stupid, so he scrambles to take up his position behind her. He strokes himself once and presses his tip against her, and fuck if he's not about to come just from the sight alone. They lock eyes in the mirror. When he slides into her they both groan.

The pause in activity has given him a second to remind himself to take it slow, to savor every moment with this woman. So instead of losing control, he starts stroking into her in languid, beautiful movements, watching her eyes darken and glaze over.

"Castle," she rasps.

"Yeah?"

"You know how at work, I'm the alpha? Well, I know it's your fantasy night, so feel free to save this one for another time, but since we're here, at work, doing really irresponsible things, I was wondering if you'd maybe, um … take control for once?"

"Why, whatever do you mean, Kate?" he asks, the glint in his eye letting her know there's a very good chance he knows exactly what she means. Still, she has no problem spelling it out for him.

"I mean that if you want to fuck me really hard, I'd really like that."

Damn.

"I fucking love you."

Castle pulls back slowly, until he's almost completely out of her, and then he slams into her so hard that the chair rocks forward. He doesn't let up, not until she's chanting out his name, and he grips her on either side of her pelvis, lifting her feet completely off the floor, giving himself to her as fast and as powerfully as he can physically manage. She feels him tense, can feel the shimmering moment he starts pouring heat into her, and they crash over the edge of their orgasms together in a spectacular and very loud explosion.

Thankfully the walls at the precinct are solid concrete.

They dry each other off with the fluffy towel in Kate's locker, dressing with thrilled and shaky hands.

Before Kate unlocks the hallway door, Castle pulls her into his arms and kisses her.

"Thanks, Kate. Best workout I've ever had."

"Mmm, me too." She sweeps her eyes down his body. Why are those basketball shorts really doing it for her? Maybe it's just because she knows he doesn't have anything on underneath them.

"Let's go home, Castle."

"After you, Detective. You know, there is a gym in my building," he suggests, waggling his eyebrows.

She laughs and shakes her head like he's the one who's insatiable.

Thoughts?