A/N: This is my first Castle fic. I had the idea for the story and thought it fitted Castle and Beckett's relationship best. Lots and Lots of fluff. I really hope you like it because I had fun trying out something new.

Disclaimer: I own nothing to do with Castle.


Kate Beckett was strong – that was an indisputable fact. But today she was struggling. Castle was just as certain of that as he was of her strength, and of the fact that she'd kick his ass if he dared to suggest that she went home. He couldn't fail to notice the dark shadows under her eyes, or the way she took a moment to steel herself before getting to her feet. He didn't miss anything, because if there was one thing writers were good at, it was observing. And if there was one person Castle was an expert at observing, it was Kate.

"Coffee?" he asked, approaching her desk with a steaming hot mug and the gentle smile he reserved just for her.

"Thank you," she replied, glancing up from her desk and pushing her fingers through her hair, causing the soft waves to fall across her face. Her voice rasped a little. He'd have found it unbearably sexy, had it not been a further sign of her exhaustion.

"Are you okay?" he frowned, as he brushed her hair away from her face, allowing his hand to linger over her forehead long enough to feel the radiating heat. "You're hot," he remarked. "Even more so than usual," he added after a brief pause.

She chuckled – of course he couldn't resist that joke.

"I'm fine, Castle," she insisted, with a smile that didn't quite reach her eyes. "I just have a lot of work to be getting on with."

"You're a terrible liar, Detective," he responded, kissing the top of her head. He knew there was no arguing with her and determined that the sooner he left her in peace, the sooner she'd finish her paperwork and the sooner he'd get her home. "Call me if you need my genius mind to lighten your workload," he grinned, as he stepped away.

She watched him leave, taking a sip of her coffee and letting the warm liquid soothe her dry throat.

"Hey, Castle?" she called, the croak still noticeable in her voice.

Immediately, he paused and turned back towards his fiancée, ready to attend to whatever need had arisen. A slight twinkle was evident in her tired eyes.

"Make sure you don't get your ego stuck in the door," she smirked, biting her lip teasingly.

He feigned hurt at her remark, before continuing out of the bullpen. At least his Kate was still there, behind the pale skin and fever.

/


The day progressed and Kate's workload only increased. Her paperwork had been abandoned when they picked up a case, and now, as the afternoon wore on, Beckett leaned heavily against a desk as she tried to make sense of the murder board.

"You let that genius know that it's welcome anytime it wants to come out," she remarked as Castle came to stand beside her.

"There are other homicide detectives in New York," he stated, as non-confrontationally as possible, as he discretely passed two Tylenol tablets into her hand. Just moments before, she'd been furiously rubbing her temples. And he could tell that her fever was bothering her – she'd had her jacket on and off multiple times in the past hour. "You could sit this one out."

He waited for the furious outburst but her response was unexpectedly calm.

"I already said I'd take the case; we just need to catch a break." She swallowed the pills with the remnants of a cold cup of coffee, just as Esposito and Ryan appeared in the room.

"Everything okay, Beckett?" Esposito asked, noticing Castle's frown and Kate's odd demeanour.

"Everything's fine," she replied with forced energy, as she straightened up and fixed her expression into a mask-like representation of her resolve to push on. "Have you got something?"

He watched as she busied herself dealing the new information and organising the other detectives, not once letting her face slip to show her exhaustion or discomfort. She was such an infuriating and stubborn woman. Damn, he loved her.

/


/

It was late in the evening and Castle once again watched Beckett. She was in Gates's office, biting down on her lip as she listened to the Captain's lecture. They'd caught that break and found a suspect. Unfortunately that suspect had been rather uncooperative during interview. Kate had lost her temper and the suspect's lawyer had complained. She'd not done anything wrong; she'd just been a little…

Hot-headed.

Yes, that was the word that Castle had heard Gates use to describe the detective, before she hauled her into her office with a stern expression on her face.

"…apologise to Mr Anderson in the morning," Gates's voice emerged from the office as Kate opened the door and Castle caught the end of the conversation. "Now go home, Detective," she instructed.

"Yes, sir," Kate replied, avoiding eye contact with her boss or with Castle. Her eyes prickled with unexpected tears of exhaustion and embarrassment.

"Kate," Castle called, as she made to walk straight past him.

"Not now," she muttered, unable to face any teasing about her being pulled up before the headmistress. She threw her bag over her shoulder and headed straight for the elevator. "I thought you wanted me to go home," she called back to Castle, in a voice too scratchy to accurately convey her intended exasperation with the day.

Without another thought, he folded his jacket over his arm, and hurried after her. Sick, exhausted and pissed-off Kate needed him. Whether she was ready to admit it or not.

/


/

A couple of hours later, Kate was curled up on her side of the bed, still fully clothed and experiencing a rare moment of self-pity. She'd been there since they returned to the loft and was becoming increasingly uncomfortable with her high temperature, pounding headache and raw and scratchy throat. But she was too exhausted to move and too headstrong to ask for help.

"Kate?" Castle's voice called, checking if she was awake as he entered their bedroom. She failed to respond but he could tell from her position that she was unlikely to be asleep. "Kate?" he repeated, settling himself, and the tray which he carried, on the bed beside her. "I brought you dinner – are you hungry?"

"No," she mumbled. "Sorry, Castle."

"Just turn around," he insisted, and she heard the hint of a smile in his voice. He steadied the tray as she slowly rolled over and pulled herself into a sitting position.

Despite her discomfort and her general dislike of how the day had turned out, she couldn't help but respond to the sight that met her with the flicker of a grin.

"You made me macaroni and cheese," she commented softly.

"That I did," he smiled, lifting the dish from the tray and passing it to her.

"Have you been talking to my dad?" she asked, suspicious of Castle's source of culinary inspiration.

"What makes you say that?" he smirked, attempting to look innocent.

"He used to make it to cheer me up when I was sick," she replied.

"I thought you weren't sick?" Castle responded, with raised eyebrows. She sighed realising that she had been caught out. He chuckled and leaned over to kiss her warm forehead. "I told you that you were a terrible liar."

"I like the added Castle touch," she remarked, trying to divert his attention from her health. She indicated the cut-up pieces of toast which had been arranged in the shape of a smiley face on top of the pasta.

"Well how could you not feel better when your food smiles at you?" he grinned.

"You know, I'm really not very hungry," she told him, turning more serious.

"Try a few bites? For me," he mock pleaded, putting on his very best puppy dog face.

She laughed and shook her head, but picked up the fork and took a small mouthful of pasta from the plate. It was true that she had very little appetite, but the small amount she could eat was instantly comforting. Or maybe it was just Castle that made her feel more like herself.

/


/

"Today sucked," Kate mumbled quietly, as she lay in bed, wrapped in Castle's arms. It was an hour or so after he appeared with the macaroni and, while she still felt a little shivery and incredibly tired, she was more comfortable than she had been all day.

"Technically, it's not today anymore," he replied, glancing at the glowing digits of the alarm clock, which read 1:37. He gently stroked her hair, feeling satisfied that her skin felt cooler than earlier in the evening. The Tylenol and lukewarm shower had done their job.

"Good," she replied, thinking of her unfinished paperwork, the as yet unresolved case, Gates's telling off and the onslaught of all her flu-like symptoms. It certainly wasn't a day she was sad to leave behind.

"Tomorrow will be better," he informed her, with a certainty that she was sure came from many nights of telling Alexis the same thing.

"How do you know that?" she asked, with a yawn and a shiver. He pulled her closer and she leaned in against his warmth.

"Because tomorrow, Detective Beckett, you will be kept under house arrest, with the great Richard Castle to take care of you."

"Rick!" she protested weakly, too tired to explain the hundred reasons that she had to be at work.

"Do you really think I'd let you leave this bed so soon after I got you into it?" he teased, whispering breathily beside her ear. The teasing came naturally, even though he knew the bed would be used for little more than sleeping for the next few days.

Sleepily, she elbowed him in the ribs, causing a feigned squeal.

"Apples!" he cried.

"Goodnight, Rick," she muttered, shaking her head, but with a smile playing on her lips as she snuggled close to him.

"Night, Kate," he replied, once again placing a kiss on her head.

"Thank you," she breathed, as her eyes fluttered shut. "For today. Or yesterday."

"Go to sleep," he replied softly. He didn't need her thanks.

He listened to her breathing becoming slower and steadier as she fell asleep, before he too closed his eyes. People often wondered why he still followed Kate around, when he had all the material he would ever need for his Nikki Heat books, and had even managed to become engaged to his muse. But it was days like this which answered his question.

Kate Beckett was strong – that was an indisputable fact. But sometimes that wasn't enough. And on those days, she needed someone who could spot the signs that strong did not mean unbreakable. Castle noticed the cracks in her carefully structured exterior when no one else could. And better than that, he was able to help her to fix them.

He wasn't just watching Kate, but waiting for when she needed him. It might not happen frequently but when it did, he was ready. Always.