Castle takes the steps two at a time, not above admitting that he's eager to find Beckett. After all, he's pretty sure he's cracked the case wide open, and as the lead detective, she should know about it. Of course, there are other ways he could contact her, no reason he can't await her arrival in the bullpen by sitting patiently in his chair. Rushing upstairs to search for her is unnecessary, and any excuse he considers for choosing to do so is flimsy at best.
But when Ryan and Esposito told him Beckett was in the precinct gym, sparring with Karpowski – well, there was really no way to ignore his need to see that in person. Beckett. Sparring. In what he imagines must be curve-hugging spandex.
He should probably take the steps three at a time.
Grateful his own workout regimen has allowed him to reach the top floor with a negligible amount of huffing and puffing, Castle darts past the two locker room doors, glances at the small weight room, and follows the intimidating – and slightly adorable – grunts beckoning him forward. When he rounds the corner and she comes into view, his jaw drops more significantly than it should; he attempts to catalogue every detail before she notices him or his brain short-circuits, whichever comes first.
The most obvious observation is that she's alone, and he finds himself uninterested in where Karpowski may have gone, only thankful Beckett has been left behind to fight an oft-abused punching bag. She's facing away from him, and her position gives him the opportunity to linger in the doorway longer than he might have been able to otherwise, no second set of eyes to catch him in the act. He'd been right about the spandex, the black fabric clinging to her in a way that makes him a little jealous. The inherent absurdity of being envious of clothing doesn't escape him.
The way the morning light plays against the shifting muscles of her back is damn near poetic, the fierce stripes of sunshine emblazoned onto her skin. There's the bow of her shoulder blades and the ridge of her spine, only temporary distractions from the irresistible expanse of the back her neck, an area so rarely bared to him now that her hair has begun to grow out. He lets his eyes drop to her waist, disregarding the whisper of guilt as he continues downward to the curve of her ass with nothing but admiration for everything he sees. Well, admiration and a rather intense desire to touch. Castle swallows back the whimper threatening to make his presence known.
In addition to his appreciation for her body, still landing punch after punch without regard for the soreness that must follow, he is caught up in the sounds she makes. He wants to take the high road and remind himself there is nothing sexual about the way Beckett is groaning – she's focused on maintaining the physical shape that allows her to take down some of Manhattan's worst – but his mind is stuck in the gutter and her noises seem purely pornographic. He wonders how much better it would be to have those same sounds pressed hot against his ear.
Before his imagination can spiral any further, he takes a few bold steps forward and clears his throat. "Beckett?"
The sudden pull of the muscles in her upper body is his only hint she's startled by his greeting, and probably would have gone unnoticed by anyone who hadn't spent the past minute staring at her back. She doesn't let up, though; if anything, she picks up speed.
"What do you want, Castle? And is there a reason it couldn't wait until I finished here?"
She's still making those same noises, sexy grunts bracketing each of her questions, and it does nothing to stop his approach. "Well, I had a breakthrough about our case, but now that I see what you're up to, I'd be happy to help you with the rest of your sparring session first."
Beckett finally pauses and turns, eyebrows raised and chest heaving in a way that is not fascinating at all. "While it's kind of you to offer to be my punching bag, I'm rather content with the one that doesn't have a mouth."
"Oh, but I can be so much more than a punching bag. I can be your sparring partner."
"With no experience and a million-dollar suit?" she snorts. "Then again, that's an excellent description of how you do everything else here, isn't it?" Her smile takes the sting away from the insult, and he grins back. Besides, if he gets his way, she'll only have the upper hand for a little longer.
"I'll have you know I did plenty of sparring when I spent time practicing martial arts as research for a book, and I continued for a quite a while afterward. And, come on, there must be extra NYPD sweatpants around somewhere."
It's clear she'd like to put her hands on her hips and glare until he backs down, but the boxing gloves she's wearing make it awkward, and by the time she's thrown them to the mat, her resolve lies somewhere alongside them. There's no argument to be made against his eagerness, and though she probably thinks she's wasting her time, she stomps off toward the locker rooms and leaves him to enjoy his view once more.
When she returns, he's already removed his jacket, shirt, socks, and shoes, and piled them neatly against the wall. Castle is just nice enough to ignore the way she flushes at the sight of his body – he'll save her some embarrassment this morning – and takes the clothes she offers. Nodding his thanks, and doing his best to hide his smirk, he hurries away and comes back wearing baggy grey sweatpants and a navy t-shirt that's probably a size too small.
"Sorry, it's all I could find on short notice."
If the gaze that keeps straying to his biceps is any indication, she's not very sorry at all.
Tugging on the sparring gloves she's given him, he positions himself across from her. Though he does have some training, is in pretty damn good shape, and has a distinct size advantage, he's under no delusions of being able to kick her ass in hand to hand combat; he's mostly looking forward to proving he can hold his own, to show Beckett he's more prepared for this than other 40-something writers might be. Circling her lithe body, being allowed to touch it, and helping her toward more sexy breathlessness are just the bonuses that come with this delicious opportunity, and he can't help but bounce on the balls of his feet as she lays out some ground rules.
And then it begins. A whirlwind he will never be able to capture on paper. A fight comprised of the same synchronization they've had from the beginning, inexplicable in its precision. Together, they dance, the choreography a surprise to them both, but their bodies falling into a predestined rhythm. It's as though they've practiced for this moment with every barb traded over the past several months.
But they're only about a minute in when Castle throws a right hook she's able to anticipate, gripping his forearm and using the leverage to spin backward into his chest. She's too slow in her attempt to do anything more, and he wraps an arm around her waist to hold her there, deep breaths taken in tandem.
"How was your mystery date last night?" he growls, just as she elbows his midsection and propels herself forward.
She pivots and allows him to see the familiar blend of exasperation and mirth spread across her face, and he almost misses the first kick when she comes back at him with a vengeance, lucky to be able to catch the second when his fingers wrap around her shin. They freeze there, the silent challenge softened when he eases her leg to the ground.
He's prepared to square up again, but she steps close, her nose threatening to graze against his. "What if I told you that my date was with your book?"
The last word is whip-like, cracking when it connects with the air, and he stammers in its wake. "Really?"
"No."
Her declaration is paired with a light punch to his shoulder, a warning that they're done talking, and then they continue sparring for what feels like forever, He's doing a decent job of meeting her halfway, and he's sure he'd enjoy the exertion on a purely physical level, except that he's lost in each extension of her leg toward his ribs, and in every one of his punches dodged by the undulation of her torso. Beckett must be distracted, too. It's the only explanation for how he's eventually able to sweep her leg from behind, sending her crashing to the mat; he fails to account for his momentum and lands on top of her in the next second.
She's hot.
Well, they're hot.
Her cheeks are pink, his shirt is wet against his skin, their pupils are blown, and the pounding of their hearts is undeniable. The energy that was released in each attack and parry has nowhere to go, their adrenaline redirected. Whatever it is that has been forced to simmer since they met in March has now been set aflame, and if she's looking to quell the potential damage, squirming beneath him is the wrong way to go about it. His hips jerk forward in response, and her eyes slam shut.
"Castle, please," she whines.
Fuck. He's sorry. He's so, so sorry, and he mumbles something to that effect, pushing up to extract himself from where he's settled so perfectly in the cradle of her thighs. Then one of her hands presses roughly against his back and holds him in place, while the other snakes between their sweat-slicked bodies and finds him hard and heavy, his desire poorly disguised by two layers of cotton.
"No. Please."
His head falls forward in relief and he sucks on her pulse point, humming into her salty skin before he succeeds in breaking through her embrace to kneel in front of her and tear at his gloves. She's hurrying to do the same, and he chokes back a laugh; for someone who sauntered away from him so easily all those months ago, she's certainly impatient now. He considers mentioning it, a casual reminder that she might not be vibrating with need now if she'd joined him for a debriefing then, but he's taken plenty of cold showers with her name upon his tongue and he's in no rush for another.
She scrambles to sit up, reaching for the drawstring of his sweatpants with a curse and a demand, but he knocks her hands aside and shoves her back to the floor. It's easy to pretend he doesn't see her scowl – he's been doing it for a while now – and he tucks his fingers into her waistband to yank her pants to her knees, sucking in a quick breath when he sees the obvious arousal awaiting him. He wants to taste her, but he'll beg for that another time; impatience dictates a more straightforward encounter today. And if Castle didn't care about getting Beckett naked for this, he definitely doesn't care about undressing himself, only putting in enough effort to loosen his pants and pull himself free of his boxer briefs.
"I swear to god, if you don't-" Her complaint ends in a deep moan when he drags his tip against her, then drives forward without further warning.
Castle will pray to a slew of sex gods and offer a deal to the devil if it means he can last longer than twenty seconds inside her. She's so wet and tight and she's making sounds that have her earlier noises seeming positively virtuous in comparison. His advantage lies in being able to control their pace, steady strokes drawing pleas of more from the lips he's yet to kiss, and he focuses on bracing himself above her, even as Beckett tries to draw him closer.
At some point he realizes she's frustrated, her control limited by the spandex trapping her legs, and of course she wants to be on top. He'll be sure to reassure her later – in a moment when they're not limited to gasping single syllables – that there will be plenty of rounds during which she can straddle him and proclaim her victory over and over again.
Honestly, she won a long damn time ago.
For now, he thrusts with exhausted enthusiasm, his arms shaking until he lowers himself to one forearm and attempts to slip his other hand between them. This time, she's bumping him out of the way, taking charge of the little she can; he cries out at the feeling of her fingers brushing him where they're joined and hopes her climax is as imminent as his.
The rapid contraction of her muscles suggests it is. The way she hisses his name over several seconds while her spine arches beneath him all but confirms it. And when the hand on his back carves five welcome lines into his skin and her body locks, he surrenders to the sensation and buries himself as deep as possible until his hips finally slow.
He manages to roll to her side before he crushes her under his weight, fumbling with his boxers and sweatpants in his post-coital daze. She wriggles into her own pants, then sits up as though she's ready to spar again, and he's left watching the sunshine highlight her upper body just as he had when he'd first come to find her. Something about the observation taps at the corner of his mind, but he can't quite-
Oh, god. "Beckett, what the hell did we just do?"
She looks over her shoulder at him with a brilliant smile and an arched eyebrow. "If you really don't know, I'd be happy to show you some other time. Perhaps more slowly and with fewer clothes."
"No, I mean, I know what we did – and don't think for a second that I'll forget what you just offered – but we did it here, where we could have been caught by anyone in the precinct."
"We weren't going to get caught," she laughs. "I locked the door while you were changing."
Castle flings his arm over his face, grateful for her foresight. Then he lurches forward and sits just behind her. "Wait, did you know we were going to have sex? Did you plan this?"
Pursing her lips as though she isn't sure whether to answer, Beckett studies him for a few quiet moments, then rises to her feet and extends her hand to help him up. It's only when they're standing face to face that she leans in to press her mouth to his for their first kiss of the morning.
Their first kiss ever.
Then she slides away with a smile, moving toward the door she needs to unlock. "So, tell me how you cracked the case wide open."