They last a month.

Twenty-seven days until she gives in to him. To the constant teasing and innuendos slipped into conversations about paperwork and standard operating procedures.

Her keys fall to the hardwood as he crowds into her back, kicking the door shut. His fingers work at the buttons of her jacket, his palms hot against the thin fabric of her shirt while she stumbles backwards into the front table. He doesn't hesitate, skimming his hands down to her hips and lifting her onto the polished wood, her shoes dropping to the ground.

She uses the extra height to her advantage, angling his face up and pressing hard kisses into his mouth even as she fumbles to undo his starched shirt. A growl of frustration escapes when the edge of his badge still pinned to his chest scratches her palm and she feels his laughter under her fingers and tastes it in her mouth.

"Shut up," she hisses, scraping her teeth over the rough stubble of his jaw. "No way to treat a superior officer."

"Yeah?" he asks, lips soft against the curve of her neck, tracing a path down the deep v-neck of her shirt. "You gonna discipline me, Detective?"

The way he bites the syllables of her rank into her collarbone makes her hips arch up to collide sharply with his stomach. Her heels hook at the back of his thighs, her mouth sliding along his cheek. "Yeah," she breathes into his ear, seductive and suggestive. "All of our paperwork for a week."

"Shit, Beckett," he groans. "Not what I meant."

She laughs, sliding down off the table, hooking her fingers in the leather of his utility belt. "I know," she says, working at the buckle of the heavy belt until it falls off, the clatter of his cuffs muffled by her rug. Kate steps away from his questing fingers, tossing her shirt and dress pants over the cushions of the couch.

He trips over his shoes as he tries to get them off and chase her at the same time, scuffing the perfect shine on them and kicking one under her coffee table. She can't stop the bark of laughter from escaping as she leans on the doorframe to her bedroom, watching him run into a corner to get to her.

"You're gorgeous," he whispers into the silence of her hallway, still standing feet from her, his own shirt untucked and hanging open.

Kate hides her smile behind the cover of three fingers pressed to her lips. "You're not so bad yourself, Castle."

His chest puffs out with male pride as he sheds his shirt, leaving it in the hall as she moves into her room. He follows, looping an arm around her waist so his fingers can slide down under the band of her panties, pulling her back against him.

She gasps when he slicks two of his fingers over her, too gentle and far too soft. Too caring. It gives her too much of a chance to rethink this whole thing even as he laughs behind her at how her hips chase after his touch. She doesn't want to think.

Kate grabs his wrist, dragging him from behind her and starting to work at the zipper of his pants. The attempt to regain some of the control fails as soon as his hands span her ribs, coasting along her back until he finds the clasp of her bra. She falters, fingers curled into the elastic of his boxers, when he pushes the straps off her shoulders and ducks his head to bite at the curve of her breast, the navy cotton bra hanging from her elbows.

She arches into him on a whimper when his tongue traces over her nipple, his left arm banding low around her back as he lowers her to the bed. She forgets, in between yelling at him for making paper clip chains instead of listening to her explain how to fill in the form to send over to the district attorney's office and how he comes up with his own theme song while helping her canvass a neighborhood after that bodega shooting last weekend, that he has physical strength under the thick layer of humor and inability to be completely serious about anything.

Strength that he uses to his advantage now, his hips pressing her down into the mattress so she can feel just how badly he wants her and one hand tangling in her hair to hold her head down as he steals her breath with sharp little biting kisses. His other traces over the tense plane of her abs until his fingers nudge her underwear out of the way to brush over her clit, chuckling into her mouth when her pelvis jerks up.

He slides his fingers into her, swallowing her string of curses when he curls them as he thrusts, unhurried and as if totally unaware of how close she is already. Her breathless pants probably give her away because it takes less than three minutes for him to take her apart completely.

"Fuck," she gasps, wrapping her hand around his wrist at her ear, needing the quick anchor as her body settles back into the comforter. She feels his smile against her throat, a smug hum vibrating along her skin. When it turns into the scrape of his teeth along the curve of her shoulder, Kate shoves at his chest, planting a knee at his hip to flip him onto his back even as she hooks her thumbs into her underwear and tosses them off the bed. Kate straddles his stomach, damp thighs at his navel. "Do not even think about it," she hisses. "I do not need to explain why I have a hickey at work tomorrow."

Castle grabs her waist, his fingers still slick and wet with her, and uses his elbows to try and reverse their positions a second time.

She laughs, her knees braced on the bed so he ends up rocking to the side, growling low in his throat in frustration as she pushes his boxers down over his knees. "Nice try, rookie," she teases, rolling her hips down against his abdominals and making him groan.

Kate leans over him to get to her bedside table drawer, shuddering when he lets his lips touch the skin just under her right breast as she digs for a condom. She rolls it over him, her short nails scraping over the sensitive skin just to watch his hips jump and hear the rasp of his voice around her name.

She considers drawing it out, torturing him until he begs. Payback for his incessant chatter and constant teasing at the precinct. But his fingers squeeze at her waist until she knows there will be bruises and she gives in, lowering herself onto him.

The cocky grin disappears for the first time since he became her permanent shadow.

Kate rocks her hips forward, hands braced on his chest so she can feel him swear under her. She wants to make this last as long as possible but everything lingers at the surface from that first orgasm. He doesn't help when he settles his palm on the small of her back, tipping her forward onto her elbows with her breasts tight against his chest and the angle changes just enough that renewed fire licks up her spine.

He gets his hand between their bodies, other hand holding her in place as his thumb rubs hard circles over her clit until, with a choked cry, he pushes her back over. Even as she shudders, Castle flips them, shoves her knees up to her chest, and continues to thrust into her. When a second, bright wave hits her and she throws her head back into the pillow. She feels the sharp scrape of his teeth over her throat as he comes.

"Shit," he breathes out, rolling off her and flopping onto the other side of the bed. "That was amazing."

Her fingers curl into the comforter as she comes back into her body. She flicks at his side weakly. "Gotta clean up," she says.

The mattress dips as he gets up and she realizes after a second that he has no idea where her bathroom is. She shifts onto her stomach, head propped up by a hand. "To your left there," she directs, watching his ass as he heads across the hall.

When he returns, he crawls over her and slides under the covers. She can tell he wants to tuck her into his chest but he stays on the other side.

After he falls asleep, she turns to face him. Gone are the lines of worry and stress around his eyes and mouth, replaced with a quiet smile.

That frightens her more than the thought of being suspended for sleeping with the officer she should be training.