Author's Note: This story was written for the CastleFanfics Prompt Challenge on tumblr and for Castle Fanfic Monday.
Prompt: AU - "Are you stalking me?"

On the second day of the third week, she had had enough.

She waited in line at the coffee shop as usual, but today, after having paid for and received her cup and taken that first long rejuvenating sip, she narrowed her eyes under the brim of her uniform cap and strode over to the seats by the window.

"Are you stalking me?" she demanded in a low, dangerous voice. The large man sitting at a stool in the window startled, jerking his head around to look wide-eyed at her. She stood over him, hand on her hip, lips compressed into an angry line.

"Good morning, Officer Beckett," he said, giving her a cocky grin.

"You even know my name? That is creepy, Mister Castle," she snapped. The emphasis on his name was intended to level the playing field - to show that he wasn't the only one who knew things - but it didn't have the desired effect. His grin merely widened and acquired a smug edge.

"So, you're a fan," he observed, pleased.

"Of the genre," she huffed. "And don't change the subject. Why are you stalking me?"

"Not stalking," he denied, shaking his head. He saw her eyes dart to the open notebook on the table in front of him, and his hand came quickly up to flip the cover shut. "Research," he said hastily. "I'm observing, uh, the fine employees of the Twelfth Precinct, for book research. Important to get the details right, you know? The day-to-day work schedule of the average cop." He paused, letting his eyes drift slowly down and then back up her figure. "Not that there's anything average about you, Officer."

"Eyes up here, pal," she barked, so commandingly that he actually obeyed, his deep blue eyes flying to her face, locking with her own gaze for a long moment.

The first time she had noticed him, she'd been excited. Her favorite author, right there in her very own coffee shop - the one across the street from her precinct house; the one where she got her caffeine fix every morning! Her stomach had fluttered deliciously when she saw him sitting by the window, pen and notebook in his hands. But she had played it cool, pretending not to recognize him. She'd gotten her coffee and left, just like she did every morning. Not until she was inside the precinct, alone in the elevator, had she given in and allowed herself a brief full-body wriggle of delight, even a tiny giggle.

It was silly, maybe, to react so strongly to Richard Castle, a guy she didn't know at all except through his books. But she loved his books. They had meant more to her in these last few years than she could ever hope to express.

Plus, he was hot.

But she'd tucked away the sighting in the back of her mind, figuring it for a one-time fluke of a thing. Until the next morning, when he was there again. And the next.

The excitement of it, the nervous jitters in the pit of her stomach, had not abated at all after seeing him there several days in a row; but then one day she noticed him again in the afternoon. This time he was lounging against a signpost near the sandwich cart where she got her lunch every day.

After that, she started keeping an eye out for him, and began to realize that he was always there, every time she left the precinct house. Not just her morning coffee and her hasty lunch, but whenever she went out on patrol, or for an afternoon coffee break. Even at Remy's, on the few occasions when she went there for burgers and fries with her fellow uniforms. She kept spotting him, again and again.

She didn't know what to make of it; one minute she was sure it was just coincidence, the next minute she'd be telling herself that he really was following her around. The whirl of contradictory thoughts got her so flustered that every morning her palms were sweaty on the metal pole of the subway car as she rode to the precinct, wondering whether he'd be there again today.

And now here they were; she had finally confronted him, and was mentally squirming with embarrassment at his response. Of course he wasn't following her around specifically; of course he was observing all the cops at the precinct. That made sense. It was so stupid of her to have assumed that he was there just for her. She was nothing special. She wanted to kick herself.

He was still looking at her, smirking slightly. Ugh, the sheer arrogance of him! She struggled to regain her equilibrium, to pull on the air of authority that she'd been working so hard to develop since she became a cop. She was good at it, too. All the other uniforms deferred to her, almost by instinct.

"Fine," she said haughtily, refocusing her glare on him. "Observe away, then. But if you turn up at my home, I will arrest you."

"Not to worry, Officer," he replied with an unconcerned shrug. "I haven't broken into the NYPD's personnel files yet, so I don't know your address, and I promise not to follow you home." His smirk was still in place. "I don't even know your first name," he added, a clear hint, looking expectantly at her. She arched her eyebrows, pleased at the opportunity to regain the upper hand.

"Well, then I guess there's nothing to worry about," she said briskly, and strode out the door without looking back.

He was there in the coffee shop every morning that week, and now that the ice had been broken, he greeted her cheerfully each time. She rarely gave back more than a grumble in reply, but he was undeterred. She saw him filling his little notebook with page after page of ink, and part of her itched to know what he was writing about her and her fellow cops, but she refused to ask. She wasn't going to get sucked in. She knew his reputation, and had no interest in being another notch on his bedpost.

She soon started to notice him greeting other cops as well. He really seemed to know everyone.

Then one morning, he called out to her before she had a chance to get in the line.

"Officer Beckett, over here," he said, holding up a coffee cup in her direction. The line was long that morning, and she sighed a little at the idea of anything - even the infuriatingly intriguing Richard Castle - delaying her acquisition of caffeine, but she stepped over to him anyway.

"What?" she grumbled, but he was pushing the cup into her hand.

"Skim latte, two pumps sugar-free vanilla," he said, and smirked again, clearly very pleased with himself. Her breath caught in her throat.

"How on earth-"

"I'm a writer," he shrugged, still grinning. "It's my job to notice things."

She narrowed her eyes suspiciously and took a small sip. The coffee was perfect: exactly the way she liked it, and still hot. She didn't know what to think.

"Thanks," she said grudgingly.

He nodded, something indefinable shifting in his eyes, and leaned back against the countertop. "You're welcome. You know," he added, indicating the baristas with a tilt of his head, "you could probably flash your badge at them and get your coffee for free any time you wanted."

She gaped at him. "But ... that would be unethical."

"Oh, unethical," he chuckled, greatly amused. "Yeah, I guess it would. And you always come to a complete stop at a red light, and you never fudge your taxes."

"What?" she blinked.

"Tell me something," he said, leaning forward, his eyes boring into her. "You ever have any fun? You know, let your hair down? Drop your top? A little 'cops gone wild'?"

She rolled her eyes, firmly ignoring the sparks of electricity that skittered across her skin in response to his focused attention. "You do know I'm wearing a gun?" she snarked. Damn him, why did that grin and those eyes have to be so damn sexy?

"Why, Officer Beckett," he gasped, putting a melodramatic hand over his heart. "I've never been threatened with physical violence by a cop before."

"Really?" She cocked her head to the side. "Not even the one whose horse you stole?"

Too late, she realized that it might be a mistake to reveal that she had looked at his rap sheet. Surprise and delight spread over his features as she groaned internally.

"Borrowed," he corrected, his eyes twinkling with mirth. "And there was a perfectly good explanation for that."

"Let me guess," she cracked back, "alcohol and trying to impress a woman."

He lifted a suggestive eyebrow. "Did it work?"

She huffed out a short laugh and shook her head slowly. "Thanks for the coffee," she said, and departed.

After that, every morning, Castle had her coffee waiting for her when she arrived. It made her a little uncomfortable to keep accepting it from him, but when she tried to give him some money for it, he brushed it off.

"No need," he said breezily. "It's the least I can do for New York's Finest." So she gave in, reluctantly.

He grew bolder about following her. He made no effort to conceal himself, waiting outside the precinct house until she came out, then strolling along a few feet behind her when she went on patrol. Not every day, but most days, he trailed along behind her until lunchtime; bought a sandwich from the same cart where she got hers; and then continued following her for another hour or two, whereupon he would abruptly disappear.

She told herself that he was probably following other cops in the afternoons, and on the days when she didn't see him.

He followed her, and observed, frequently taking notes in his little book. He watched her handle shoplifters and fender-benders and lost tourists. Once, she had to break up a fight between two men and the woman they were fighting over, and afterward, when several of her fellow uniforms belatedly arrived to help her handcuff the three combatants, she caught Castle staring at her with an open-mouthed expression of awe.

"What's the matter, Castle?" she asked, shoving one of the men into line with the others for the walk back to the precinct. "Never seen a cop take down a suspect before?"

"Huh, uh, no," he stammered, wide-eyed. She sighed and rolled her eyes. Men! They were all the same: turned on by the uniform, but slow to believe that a woman who looked like Kate Beckett could have the physical prowess necessary to do the job.

"That was awesome, the way you took them down," he gushed as he followed her and the rest of the group down the sidewalk. She merely shook her head and sighed again. When she glanced back at him, sure enough, he was scribbling furiously in his little notebook again.

"I didn't see you yesterday, Officer Beckett," Castle said one morning, his expression open and curious.

She was feeling raw today, emotional, her tough shell thinner than usual, so she could only manage annoyance at him. It wasn't sweet that he would notice her absence and ask after it. No. It was just irritating.

"I had the day off," she said shortly, tossing him a quelling glare as she took a slow sip of her coffee.

She didn't need to say anything more than that. No way did he need to know anything about her personal life, anything at all about her, outside of her cop work. No way did she need to share anything with him.

"It was my mom's birthday" fell out of her mouth entirely against her will.

She immediately felt a sharp stab of regret at the way he brightened, pleasure sparkling in his eyes at the thought - written clearly across his face - that she was opening up to him.

"Oh, that's nice," he chirped happily. "What, did you take her to lunch, buy her something nice?"

Guilt and grief welled up in her and turned to anger, ashen in her mouth. "Visited her grave," she bit out, and winced hard at the way his expression crumpled into shock and dismay.

"Oh - oh god, I'm sorry," he exclaimed, but she couldn't take it. She spun on her heel and stalked out.

"Wait! Beckett, wait." She was already halfway down the block when he caught up with her, his coat and notebook clutched haphazardly under his arm.

"Hey. Wait up. I'm sorry," he said, panting a little, matching his stride to hers.

"It's fine," she said, not looking at him.

"No, hey, listen."

Sighing explosively, she stopped walking and turned to him, lifting an eyebrow. Her posture and expression radiated I don't want to talk about it and she could only hope that he would get the message.

"I," he began, and faltered briefly, and then said, "I still don't know your first name."

She breathed out slowly, some of the tension leaving her shoulders.

"It's Kate," she said grudgingly, "but surely you've noticed by now that we cops aren't big on using first names, Castle."

She resumed walking, and he fell into step beside her. No more words were needed.

It wasn't until that night, lying in bed, that she realized Castle had gone from surreptitiously following her from far behind to walking right alongside her, almost like a partner. She squirmed and blushed in the darkness of her bedroom, thinking about how natural it had felt to have him at her shoulder, matching her stride, observing. Always observing.

"Hey, Beckett," said one of her fellow uniforms, a few mornings later. "Where's your shadow?"

"What?" she asked, distracted, looking over some paperwork.

"Yeah," put in another officer, "that writer who's always following you around, when's he gonna come into the building, watch you do paperwork?" The two chuckled.

"Who, Castle?" She put the forms down and cocked her head curiously at her co-workers. "He's observing all of us."

The two officers exchanged a look. "Uh ... no," one of them said slowly, "pretty sure it's just you, Beckett."

"Bull," she said, but she was frowning.

That afternoon, as she walked down the sidewalk with Castle at her shoulder, she looked at her watch and saw that it was nearly 2:00; almost the time when he would usually disappear. "Don't you have to go?" she asked.

"I've got a few more minutes," he replied unconcernedly. She pursed her lips and decided to go for it.

"Where do you go off to every afternoon, anyway?"

"Oh," he said, looking surprised. "I have to pick my daughter from school. I thought you knew."

"Your daughter?" Beckett quickly pulled on her poker face to cover up her consternation. Apparently she didn't know as much about Rick Castle as she had thought. She vaguely remembered reading that he had a child, but she also knew he was divorced, so she'd just assumed...

"Yeah, school gets out at two-thirty," he said, pulling out his wallet and producing several pictures of a smiling little redhead with chubby cheeks and bright blue eyes just like his. "That's Alexis. She's ten. I have full custody," he added, "so if I don't pick her up, I'd have to hire someone to do it, and that just seems silly."

"Silly," Beckett echoed, taking one last look at the photos before handing them back. "Sounds like she's a lucky kid."

"I'm the lucky one," he smiled. "Until tomorrow, Officer."

"Bye," she replied, and continued on her patrol alone, her thoughts whirling.

The way his whole face had lit up, and his tone softened, when he mentioned his daughter. The casual way he said I have full custody.

The fact that he obviously wasn't spending the afternoon following other cops, as she had assumed.

Realization hit her like a brick wall. She was the only one he waited for with custom-made coffee every morning. She was the only one he followed around on patrol, all morning and half of the afternoon, almost every day.

What the hell was going on?

It took her a few more days to get up the nerve to ask him. When she finally did, she chose her words carefully and kept her tone as casual as she could manage.

"So, is all of this just background research for the next Derrick Storm book, or what?"

He took in a quick breath, glanced sideways at her, and said carefully, "Not exactly."

"What then?"

"Um ... I'm working on a new character," he said cautiously. She wondered if he was even aware that he had shifted to the side, subtly increasing the distance between them.

"A new character." Abruptly, the implication hit her, and her steps faltered for a moment as she gaped at him. "A ... a character based on me?"

"Well..." He took another half-step away, watching her warily. "Don't be mad, Beckett. It, it just kind of happened."

She stopped walking and folded her arms across her chest. "Tell me," she demanded.

His eyes darted nervously from her face to the sidewalk and back again, but he acquiesced.

"It started out like I said. I was just observing the precinct, the neighborhood, all the cops. But as soon as I saw you, I, uh." He paused, shook his head. "This is such a cliché, but you were different. I mean, you don't fit here, Beckett." He met her eyes, regaining his confidence. "Your accent says Manhattan, you clearly come from money, so you had other options. Better options. You could have been a lawyer or a doctor, but you became a cop. Why? I figured there had to be some tragedy in your past. I didn't know about your mom yet."

"So you decided to follow me around," she prodded.

"Well." He studied her, trying to gauge her reaction. "I'm here for the story. I go where it takes me."

"And you're writing a character based on me in the next Storm novel?"

"Something like that," he said evasively. She narrowed her eyes and held her glare on him until he broke. It didn't take long.

"Or, or maybe a new series," he admitted, and gulped.

Beckett could only blink, her heartbeat pounding in her ears. Was he serious? A whole new series of mystery novels, about a character based on her?

"You've got to be kidding me," she decided, and resumed walking. He joined her, slipping easily back into his accustomed spot by her shoulder.

"I'm not, but nothing's decided yet," he said quietly. "I'm still contracted for two more Storm books, and I've only written half of one so far."

"Hmm," she murmured, walking on. She could see that he wasn't telling her everything, but she wasn't sure she wanted to know what he was holding back.

"You're hoping for homicide, right?" Castle asked after a moment.

"What?"

"That's your ultimate goal, isn't it? To get assigned to the homicide division, when you make detective. So you can work on solving your mom's murder."

"If I make detective," she corrected, but he scoffed.

"Please, Beckett. You'll be there any day now. You're the best uniform this precinct has got, and everyone knows it." He looked sideways at her. "You're extraordinary. You know that, right?"

She had no idea how to respond to that. So she just kept walking.

The day she made detective was the day he kissed her for the first time.

He found out, somehow; by then he was a fixture in the precinct, having spent enough time in the coffee house and at Remy's that all the uniforms and clerical staff, and at least half of the detectives, knew him. So someone tipped him off, though she never found out who. In any case, when she came out of the building for lunch, glowing with the excitement of her promotion, there he was at the bottom of the stairs with a little bouquet of flowers in one hand.

She hadn't taken off the uniform - didn't have an appropriate change of clothes in her locker - but she had removed her hat and attached her shiny new detective badge to her belt. Castle spotted it and beamed, holding out the flowers. She blushed and ducked her head bashfully.

"Congratulations, Detective Beckett," he said softly. She couldn't contain her own smile at the new, unfamiliar title.

"Thanks, Castle." She accepted the flowers, and when she looked back up at him, he was closer than she had realized. A lot closer. Right in her face, in fact, and she didn't back away when he leaned down and pressed his lips to hers, lightly at first, then more firmly when she leaned into him.

His hands slid around her back, broad and hot, and his tongue traced the outline of her lips, dipping inside when she opened her mouth to him. She could taste the coffee on him. His hot wet mouth was delicious, and her whole body sizzled with pleasure, goosebumps prickling across her skin as she kissed him back. Her pulse sped up as his tongue slid along hers and her free hand curled around the back of his neck.

After a long moment he pulled back, grinned into her eyes, and said hoarsely, "Remy's?"

She dropped her hand away from him and hid her smile behind the flowers. "Yeah."

Lunch was a boisterous affair: Remy's was full of cops, and everyone had heard about Beckett's promotion, so they had a loud and constantly shifting crowd of companions joining them, surrounded by chatter and laughter. It was friendly and fun, but Beckett was grateful to finally escape to the relative quiet of the sidewalk outside.

"So," she said carefully as she and Castle walked slowly back toward the precinct house, "I guess you won't be following me around any more."

"Oh, you never know," he replied with a secretive twist of his lips. "I still have a few tricks up my sleeve."

She turned to him, about to ask what that meant, when he burst out with, "Beckett, will you come to dinner with me tonight? Just the two of us."

Heat rushed across her skin as she thought giddily, Richard Castle just asked me out. She couldn't help remembering the kiss and how good it had felt to press her body against his, the strong bands of his arms around her back, the intoxicating taste of his tongue.

"Okay," she managed through a dry throat. He grinned and bounced a little on his toes with pleasure, pulling out his little notebook. He flipped it open to a blank page and handed it to her, along with his pen.

"Still not a stalker, but I do need to know where to find you," he said, his eyes twinkling. She rolled her eyes at him, but took the pen and wrote her address.

"Pick you up at seven?" he suggested, tucking the notebook back into his pocket. She nodded slowly, her gaze fixed on his mouth. Was he going to kiss her again? She wanted him to. Oh, how she wanted it, even though they were standing right outside her workplace with dozens of curious eyes coming and going.

They gravitated slowly closer to each other, leaning in -

"Detective Beckett!"

She startled back from Castle, her head whipping around to see her new boss, Captain Montgomery, coming down the stairs.

"Sir!" she exclaimed, snapping to attention.

"You've caught a case, Detective. Let's go."

She turned wide eyes toward Castle. "My first homicide," she breathed, a whole new kind of excitement spreading through her. She could see it reflected back at her in Castle's eyes.

"Go on then. Knock 'em dead." He paused. "Well, they're already dead." The familiar smirk was back. "Too soon?"

She bit back a snicker and reached out, brushing her fingertips along the back of his hand.

"See you tonight, Castle."

"Until tonight, Detective."