Author's Note: I saw a bunch of people on Tumblr post how they wanted to see an AU Castle fic with Castle as the detective and Kate as the writer, so I thought about it and this idea popped into my head. It's kind of a hybrid of Castle and the Nikki Heat books, except reversed and with some of my own changes.

He's the detective; she's the writer. AU. 20 Chapters.

One

Five a.m. in New York City. The sun had just begun to coat all the east-facing windows with glowing busts of orange. All the partying twenty-something's had barely fallen in to bed, and the hard working men and women of the Borough of Manhattan were beginning to arrive at work. Among them sanitation workers, delivery drivers and Detective Richard "Castle" Rodgers.

Even at that early hour, a rising heat could be felt off the pavement and palpable thickness hung in the air. A week earlier, July had plunged the city into an unrelenting heat wave of one hundred degree plus days, blazing sun, and no rain to speak of. Fortunately, the weather man predicted a break in the weather by the weekend, but that was still three days away. Until then, they were stuck with a heat index rising to a sultry one-oh-five.

As he approached the yellow police tape, the detective tucked one finger between his shirt collar and Adam's apple attempting to loosen the garment already clinging to his damp flesh. Being forced to dress in a shirt and tie every day by a C.O. who always wanted everyone to look professional was bad enough, but in the middle of summer? It was a total bitch. At least he'd been wise enough to pick up an iced coffee before hopping the subway uptown to the scene. Then again, in this heat the ice would be melted by the time he reached the body.

"'sup Castle," Detective Javier Esposito greeted him as he lifted the tape.

"Morning," he replied cheerfully, ducking under the barrier. "Dino here yet?" he asked, referring to his partner, Detective Sal Dennison, fondly referred to as "The Dinosaur" or "Dino" for short.

"Just rolled in, sweat stains and all," Esposito said, nodding towards a tight cluster of uniformed personnel.

Castle approached the cluster of five men, Dino plus two uniformed officers and two members of the CSI squad, and took a deep breath. He knew they were standing in front of the body and he wanted to make sure he had a good hold on his Egg McMuffin before he caught his first glimpse. Nearly ten years on the job—four of them as a detective—and he still had trouble getting used to blood and gore at early hours in the morning. "Sal," he greeted his partner with a nod (of course they never called him Dino to his face!).

Sal turned his thick neck in Castle's direction revealing the already dampening spots around the V of his collar; Castle suppressed a grimace. "Managed to drag yourself out of bed for this one, eh Ricky-boy?"

He forced a smile, loathing the way he was called "Ricky-boy" more with every usage. "It was a struggle, Sir, but I managed." Two years into their partnership and Castle was still loathing every minute of it, but his time of suffering was nearly over; The Dinosaur was slated to retire at the end of the year. "What've we got?"

"Jane Doe, mid- to late-twenties, deceased approximately four to six hours," Sal informed him.

"COD?"

He nodded towards the body. "Take a look for yourself."

Castle stepped around his partner and approached the sidewalk. Propped up against the wrought-iron gate in front of a modest brownstone was the young woman. Blonde, dressed in a green dress—the classy party-going kind, not the streetwalker kind—and matching heels. Though her face appeared pristine, a massive cut ran from one ear to the other under her jawline, coating her pale skin from the neck down in dried maroon liquid. "So…cause of death was exsanguination?"

"Looks that way," M.E. Lanie Parish replied from her position crouched beside the body. "I have to get her back to the lab to see if there are any other injuries or bruising, but she was definitely alive when her throat was cut. A wound like that," the doctor paused and shook her head, "she would have been dead in a minute, tops."

Castle approached the body so that he stood only a few inches away from the victim's feet. He crouched down and examined the details as he always did. Obvious injuries were one thing, but he looked deeper than that. What was in her hands? What was in her hair? How was the body positioned? All these questions led to the clues needed to solve these heinous crimes.

His eyes glazed across the sidewalk on either side of the body. Like every other street in the city, it was lined with bits of trash, foliage, and smashed substances. Despite this grime, a clear splatter pattern of red could be seen. "She was killed here," he concluded aloud, "but the killer posed the body propped up like this against the fence."

He stood, facing the direction of the spray, putting himself in the shoes of the victim. "The killer came at her from behind, slashing her throat, then turned her body to put her back against the fence." He turned toward the nearest CSI tech and said, "Make sure your guys check for any shoeprints tracking the blood splatter in a certain direction."

He walked to the other side of the body, where the M.E. had been crouching and reviewed the scene from that angle. The woman's arm was down at her side, wrist and hand resting on the sidewalk. When he examined them from this angle, he spotted something odd. "Dr. Parish? Can you please hold up her hands?"

The M.E. did as he asked as he stroked his chin. "Odd," he said.

"What?"

"Her fingernails," he said. The nails were all painted a dark color—black, possibly, or a deep purple—except for one. The middle finger of her right hand was naked, unpainted. He considered this for a moment. It was possible that if her nails were acrylic, the middle one had fallen off, but that scenario did not feel quite right to him. "I'm not expert, so perhaps you could tell me—are her nails fake?"

"Hmm," she said, lifting the hand up to examine it. "No, they look natural."

"And do the other nails have any chipping or missing polish?"

She examined both hands and concluded, "No, not really."

"Then why is her middle finger completely unpolished?"

"I don't know, Detective."

Castle rocked back on his heels as he thought. Curious, very curious. "Again, I'm no expert, but tell me Doctor. If you were going out for the evening, such as to a party or a gathering with friends, would a woman such as yourself go out with her nails in such a state?"

"Absolutely not," she concluded.

"Ricky-boy!" Sal called out. Castle groaned inwardly as he watched the rotund man approach, making great effort to step up the three inches it took to move from the blacktop to the concrete. "The body was found by that dog-walker over there and I-"

"Detective Dennison?" one of the uniformed officers said as he approached. "There is a reporter here being quite persistent about asking what's going on here. Would you like to speak to her?"

"A reporter, eh? You better handle this one, Ricky-boy," Sal said, clapping him on the shoulder. "Just remember-"

"Don't tell them too much—I know," he said, unsurprised that Dino, the known sexist, did not want to speak with a female reporter. Normally he jumped at the chance to be quoted in an article—assuming it was a quote that made him look good—but dealing with women was the exception for this.

"She's on the other side of the M.E. van; said her name was Beckett," the uniform said.

Castle nodded a thank you at the man and then stepped off the sidewalk. Dealing with reporters was not his favorite part of the job, but it had to be done and there was no escaping it. He tossed his now-empty coffee cup in to the nearest trashcan and wiped his damp hands off on his pants as he circled the M.E. van, staying inside the circle of caution tape.

As he came around the corner, he spotted a woman in a grey pantsuit, her chestnut hair twisted in to a bun at the nape of her neck. She faced away from him, presumably making sure she stayed clear of the patrol vehicle speeding away from the crime scene, lights and sirens blasting. "Excuse me," he called, "are you Ms. Beckett?"

At the sound of her name, she spun around and the moment he locked eyes with her, he froze, feeling as though he'd been shot directly through the heart. As she brushed a strand of bangs out of her eyes, he realized that she was without a doubt the most beautiful creature he'd ever seen. Chocolate eyes, full skin, and sun-kissed skin peppered with freckles across her nose and cheeks; he was captivated.

"Yes, hello, my name is Kate Beckett; I'm from the New York Times and I was wondering if I could ask some questions Detective…." She let her voice drop off, obviously as a lead-in for him to give his name as she held up her iPhone, recording ap already started.

"I-uh-I," he stammered for a moment, for some reason unable to respond to her implied question. When she arched her eyebrows curiously at him, he cleared his throat in an attempt to regain his composure. "Hi, sorry, hi I'm Detective Rick Rodgers, but everyone calls me Castle."

"Castle?" she echoed, extending her hand to his.

"Yeah, Castle. I—oh, you have very soft hands," he concluded as theirs joined together.

"Um," she said, yanking her hand back rather suddenly. "Thanks. So what can you tell me about the victim?"

"Well, not much. Jane Doe—no ID with the body—and she was killed around midnight."

"Was she shot?"

"No, her throat was slashed."

The reporter nodded, appreciating the way he did not pull punches as so many of the other cops did when speaking with her, a so-called delicate female. "Witnesses?"

"I'm sorry," he said, giving his usual fake press smile. "That's really all I can tell you at this time."

She gave him an annoyed look. "Well you didn't tell me much of anything."

"Right. And that's all I can tell you at this time," he said, maintaining his even voice the best he could. He nodded to her and turned away but she stopped him.

"Wait!" she called out. "Here's my card. If there's anything else you can tell me."

"Yeah," he said, snatching the card out of her hand and tucking it into the breast pocket of his shirt. "I'll be sure to call right away."

He strode away from her, not looking back, but wondering briefly why someone as pretty as her chose such a slimy profession. True, he had not had any negative experience with the press, but it was simply a fact of life: until the day when cats and dogs shared their kibble together, reporters and cops would never see eye to eye.