A/N: This originally began as nothing more than a product of an awful cold that I came down with recently, but quickly grew into something quite a bit longer than I had expected. Hopefully, it's not as dreadful as I felt while writing it.

Set mid season 4.

When Beckett returns from her interrogation with their suspect, she notices the empty chair at the side of her desk has been filled by its owner. Her heart hastens at the sight, a smile spreading across her lips without her permission, and it's silly, especially if she considers the fact that she sees him practically every single day, but when he had failed to answer her usual call for a body in the morning, she hadn't expected for him to show up today. She'd even been irrationally worried at the lack of response, so to be proven wrong now is for once a pleasant surprise.

"Hey Castle," she greets, allowing herself the brush of her hand to his shoulder as she passes. "Didn't think you were coming in."

Kate glances up from her desk chair at his lack of answer, her brow creased at the unusual silence, but once she finally sees him, it all makes sense.

His bleary eyes blink, struggling to focus on her, but once they find her, they flicker with light, dull but alive in the pale blue of his irises.

"Beckett, sorry I'm late," he croaks, attempting to clear his throat, ending up in a coughing fit instead.

Kate flicks her gaze towards Gates' office, relieved to see the blinds shut tight, and slips into her seat, rolling her chair in closer to Castle's.

Her hand flies to his forehead before she even realizes what she's doing, but his damp skin and fevered flesh steal her attention from the meaning behind her unplanned touch and that familiar worry uncoils from its hiding place inside her stomach.

"Castle, you're burning up," she murmurs, withdrawing her hand, but keeping her eyes on the deflated man in front of her.

"Not so bad yourself," he quips, quirking his brow for her, but it does nothing to mask the misery lining his bloodshot eyes and flushed skin.

"You have a fever," she corrects, grabbing his knee in hopes of holding his fading attention. "You barely look like you can sit up. What are you doing here?"

"Partners," he shrugs, practically slurs. "I wanted to help solve the case and I feel fine."

Kate rolls her eyes and slides open her bottom desk drawer, already digging for her keys.

"Hey Castle," she hears Ryan announce from behind, trotting up to her desk with a triumphant grin.

"Did you see Beckett and I crack that guy wide open?"

"I missed it?" he whines, slumping forward and dropping his head to rest on the edge of her desk.

Ryan cocks his head in confusion. "What's wrong with him?"

"He's sick," she mutters, fishing for her car keys and rising from her chair. "And now I have to take him home."

"It's just a small head cold, Beckett," Castle protests from the pillow of his forearm. "I don't need to go home."

"I'll be back for the paperwork," she informs Ryan, but her coworker waves her off.

"Don't worry about that, just get Castle out of here before he infects us all."

"I'm not contagious," Castle adds on a huff, eliciting a smirk that curls along her lips while she coils her fingers at his elbow, tugging until he finally relents and sits up.

"C'mon Castle, might as well let me escort you out before Gates sees you and lectures us all."

"Should I tell Javi to cancel your lunch order?" Ryan inquires, stepping in to help her get Castle to his feet through his grumbling protests.

"Yeah," she sighs, her concern doubling over at the shake of Castle's bones beneath her hands, the tremble of his body against her side. "I may stay with him for a while, make sure he's okay."

She expects a teasing remark to follow from Ryan, a retort about how she'll be spending her afternoon taking care of Castle, but Ryan appears just as worried as she feels when she spares a glance in his direction.

"I think that's a good idea."

She walks Castle to the elevator with relative ease, their pace slow but steady, and he sighs in relief once they're inside the lift where he can prop his body against the nearest wall.

"Okay, so maybe staying home would have been a better idea," he concedes, wincing through a swallow. "Just stick me in a cab, I'll be fine."

"No," she argues, too quick, earning a tired arch of his brow, but she doesn't care. "You can barely stand, I'm not just going to put you in a cab and assume you'll get home safely."

"But Beckett-"

"Like you just said, partners," she reminds him, feeling the heat radiating from him in waves as she steps closer. "Are Alexis and Martha home?"

His head lolls in a halfhearted shake. "Alexis has class and Mother's… not sure where she is, but the loft is empty."

Kate purses her lips, coiling her fingers around his elbow once again when the elevator doors part for them. It was still early in the day, probably hours left before his mother or daughter would return, and she really shouldn't cut out from work like this, but she could still remain on call, still rush back if she was needed.

"I'll just stick around until one of them gets back," she assures him, assisting him in the potentially perilous journey down the sidewalk to her Crown Vic.

"I'm not a kid, Beckett," he sighs, relinquishing his arm from her grasp and managing a smooth entry into the passenger side of the vehicle.

Kate rolls her eyes, a teasing quip already on the tip of her tongue, but as she watches his head fall back against the headrest of the seat, his eyes squeezed shut and his mouth in a deep frown, she swallows the remark down. She had always thought if an opportunity like this ever arose, he would be all too ready to needle her with jokes about playing nurse, to use his inherited flair for dramatics to take advantage of a chance for sympathy, but right now, Richard Castle isn't playful at all. He's miserable and it's gut-wrenching to witness.

By the time they arrive at his loft after a twenty-minute drive through midday traffic, Castle has fallen asleep with his forehead smudged against the passenger window, his neck craned in a way that has to be uncomfortable. Kate sighs and unbuckles her seatbelt, unfastens his next and carefully eases her palm beneath his cheek, coaxes his head away from the window so she can free him of the safety belt.

His skin is damp beneath her hand, the heat emanating from his forehead reaching worrisome temperatures, and Kate bites her lip, brushes the sweaty ends of his hair back from his face. She needs to get him inside.

"Castle," she calls softly, lifting her other hand to aid in supporting his head, stroking her thumb along the warmed shell of his ear. "Rick, wake up."

His brow furrows and his face twists with displeasure as he swallows. "Beckett."

"Yeah," she murmurs, watching his eyes peel open to find her, so dull and hazy with exhaustion, but they come alive with recognition for her, with gratitude, and she has to remember to withdraw her hands from his fevered skin, has to remind herself to ignore the stupid, inappropriate butterflies that were born from a conversation on a swing set and have multiplied within the few months since.

"Probably should have stayed home," he rasps, having to clear his throat with great effort to clear the congestion forming there, stealing his voice.

"Probably so," Kate confers, but she offers him a small smile while his gaze is still trained on her, still clinging to the last of his coherency. "We're back at the loft now though, so come on. Let me take you inside."

"You said-" He does his best to turn away as another painful sounding coughing fit overtakes him, shaking the entirety of his frame, and she reaches for his curved spine, spreads her hand between the trembling wings of his shoulder blades. Even through the barrier of his coat, she can feel the heat radiating from beneath his clothing. "You were thinking about staying?"

He doesn't meet her eyes when the question scrapes past his lips, his unfocused gaze fluttering to the floorboards, because… oh, he doesn't expect her to stay with him. And that hurts a little, but she can't blame him. She couldn't stay for him that day in the cemetery, why would he believe she could now?

Kate inhales sharply through her nose, reins herself back in from the spiral of those dangerous thoughts, and curls her free hand around the door handle instead. She retracts her palm from his back and exits her cruiser, strides around the front of the car until she's on the passenger side and can tug open his door. Castle glances up to her in confusion, as if he isn't quite sure how she got there, but he takes the hand she extends down to him, allows her to haul him up and assist him in exiting the vehicle.

She nudges the car door shut with the toe of her boot and feels Rick's breath rattle through his chest when she bands an arm around his waist.

"I'm staying, Castle."

The nausea and dizziness roll through him in waves, turning the trek through his lobby into a wobbling struggle, her arm clenching around him each time his balance starts to waver, her hand waving him off every time he starts to mumble an apology. The journey down his hallway is a little less perilous, a lot quicker too, and once he fishes the keys from his coat pocket, she's finally able to guide him inside his home.

"Bed or the couch?" she murmurs, holding him steady as they sway in the foyer together.

His eyes keep closing, his face threatening to go slack, and Kate lifts a hand to his flushed cheek that's starting to fade into a sickly pallor, watches his eyes flare open, immediately searching.

"Hey." Blue and unfocused, but shimmering with soft delight, his gaze trips down to land on her.

"Kate. Hi," he sighs, a dopey grin managing to spread across his lips and she chuckles, smoothes her thumb along the paper thin skin beneath his eye.

"Do you want to rest on the couch for a bit? Eat something?"

Castle shakes his head once. "I don't think I can. Just – need to lie down."

"Bed it is then," she nods, rubbing her hand up and down his spine, waiting until he seems ready, steady enough to begin the walk to his bedroom.

They maneuver around his loft far easier than the rest of his building, the path he shuffles through well practiced, and she could let him go. She should probably let him go. He doesn't need the pillar of her body like a crutch at his side anymore, but she remains glued there nonetheless, up until they reach the threshold of his bedroom.

It isn't how she imagined her first time entering the most intimate space of his home, but she takes the opportunity to admire the room bathed in strips of daylight from the half closed curtains, appreciating the chance to be surprised by how much she likes the style, the subtle masculinity and underlying earth tones decorating the walls. She could picture herself here, more clearly than she ever could before.

"Beckett?"

She startles, realizes she's just been standing with him in the doorway, halting his progress towards the bed, and yeah, she really should have let him go.

"Sorry," she murmurs, leading him towards the unmade bed in the middle of the room and aiding him in his descent to the side where the comforter is pulled back and the sheets are crinkled with use.

Easing his jacket from his shoulders and helping unfasten the buttons of his dress shirt that his fumbling fingers miss is not how she pictured her first time undressing him either. Even in his state of illness, she thinks Castle must share the thought, his cheeks darkening from their blotchy shade of pink to an embarrassed scarlet hue. Relief seems to trump awkwardness once he's in only his undershirt though, the cool air a welcome balm to his burning flesh.

"Do you have a thermometer? Something to take for the fever?"

Castle is already listing back against the headboard, eyes fluttering shut, but his hand twitches, lifting to point towards the en suite. She locates a bottle of Tylenol in his medicine cabinet, a thermometer in the second drawer of the vanity. He's barely coherent as she slips the thermometer past his lips and fills the glass on his bedside table with fresh water while she waits for his temperature to be revealed.

"Jeez, Castle," she mutters to herself when the stick beeps from his mouth.

102.5 is just shy of a high grade fever.

Kate withdraws the thermometer, sets it down on his nightstand for now, trading it in for the water and pill bottle instead. She has to hold his chin up while he swallows, even as he raises his hand to support the glass. His movements are too slow, too sluggish and uncoordinated, as if he no longer holds the control over his own limbs.

"Just a cold," he insists while she helps him lie down. "Be fine, Beckett."

She notices too late that she is in the process of tucking him in, pulling the soft fabric of the comforter up to his shoulders and stroking his dampened hair back from his slack face. He tilts into her touch, hums low in his throat and snakes his hand from beneath the covers to loosely cradle the back of her hand.

"But don't go," he sighs, his eyes slitting open to stare up at her, tired but so adoring. "Don't want you to go."

His inhibitions are lowered, she knows that, knows he likely won't remember half of what he's said to her today, but her heart still cracks at the gentle pleading in his strained voice, the trace of hope that fades all too quickly. She hadn't intended to leave in the first place, hadn't wanted to, but now her decision has been solidified.

Kate crouches at his bedside and leans forward, pressing her lips to his forehead. His skin is scorching, but she lingers there, breathes past the scent of sweat and impending sleep clinging to his flesh, breathes in the familiar comforts of coffee and his aftershave still present beneath the layer of fever.

"I'm staying, Castle," she promises, feeling the rise and fall of his chest begin to even out, his breath flowing in a steady rhythm past his parted lips. "Not going anywhere."