Author's Note: Keep reading and reviewing! This is so much fun to write...

Much to Richard Castle's dismay – and surprise – the mayor couldn't help him this time. Apparently, his request to locate one specific detective in the city, and his lack of adequate reason for doing so, was a bit strange – if not slightly stalker-ish. As big a fan as Bob Weldon was, Castle supposed there were favors even he couldn't cover.

Which left Castle with more unconventional options, and what was more unconventional than a private investigator who only kept nighttime hours? He'd found the address in the phone book – yes, those things still exist – his writer's curiosity piqued by both the unorthodox hours and the fact that this agency specialized in strange cases.

With any luck, "strange" meant supernatural.

It was almost midnight by the time Castle made his way to the fourth floor of the nondescript office building in Midtown, rounding the corner to his left before finding the door in question. It was cracked open, the name of the agency etched into the clouded glass window. Eyeing the name, making sure he was in the right place, Castle rapped his knuckles against the frame.

"Hello?"

The man sitting at the desk several feet from the door looked up from the book he'd been reading. His skin looked pale under the moonlight spilling in from the windows running along the wall to his left. Wearing a black button-down and black pants, the man sat up a little straighter, his brown hair standing up in the front.

"Welcome to Angel Investigations," the man announced, his lips curling into an awkward smile. "I'm Angel. What can I do for you?"

Crossing the threshold into the office, and taking a seat in one of the leather chairs sitting across from the desk, Castle reached into his black overcoat and pulled out the stake he'd found the previous night. "I'm looking for someone," he explained, holding up the weapon. "The owner of this, actually. I'm afraid she misplaced it last night."

Angel's awkward smile faded when he laid eyes on the stake, sitting up a little straighter in his chair and clearing his throat. "And how did this happen?"

"I was in an alley last night – I know, I know, alone in a dark alley at night, not the brightest idea – but I stumbled across a vampire attacking a woman, and the thing turned its attention to me instead." Castle's voice rose as he spoke, as if he was getting more and more excited in recalling the ordeal. "This woman swoops in, kicks its ass, kills it, and leaves without this."

"I see." Angel leaned back in his chair again, his right index finger trailing back and forth over his chin. "Does this woman have a name?"

"Kate Beckett."

Angel's shoulders relaxed and a smile crept back onto his pale face. "Detective Beckett."

"Yeah." Castle's brow furrowed in confusion. "You know her?"

"C'mon, what kind of PI would I be if I didn't have a working relationship with the police?" Never mind the fact that Angel's first experience with the police as a PI – all the way back to his early days in Los Angeles – had been something more akin to a disaster. Fortunately, his experiences with Detective Beckett had gone far better.

Three years ago…

Business had been slow for Angel Investigations, and Angel told himself that was simply because it was still so new. He'd only been in the Big Apple for six months, and after his ordeal with Wolfram & Hart, it only made sense to eventually get back to his roots. It felt wrong doing this without his crew, his family, but the fact remained: there was no one left.

Wesley and Gunn were dead. Cordelia had passed long before them – though her picture hung off the wall behind his desk, a constant reminder of his need to fight the good fight and to never forget who he was.

There was no telling where Spike ran off to after the battle with the Circle of the Black Thorn; last he remembered, Spike was serving as a guide of sorts for Illyria. As had often been the case over the centuries, Angel was on his own – and truth be told, he didn't particularly mind.

The door to his office opened, and Angel looked up to see a thin woman, disheveled and bloodied, staggering into his space. Her hair was short with a hint of red, a trail of dried blood ran from her nose to her upper lip. The woman favored her right shoulder, her arms cradled over her stomach as she walked with a slight limp.

His eyes instantly went to the gold badge clamped to her hip, before he noticed the large-faced black watch on her left wrist and a silver chain around her neck. The woman lowered herself into one of the chairs across from Angel's desk with a cringe, tucking her legs under herself. By the time her tired eyes flicked up to his, Angel could see the darkness in them.

"Miss…"

"Are you Angel?" Tired though her eyes were, they were still full of determination.

"I am."

"I hear you handle the weird stuff."

Angel leaned forward in his chair, his elbows resting on the surface of his desk. "Define weird."

"I don't know what I am." The woman stared at her hands, and Angel could see dust and ash caked into her nails. "I have trouble sleeping sometimes. Dreams. Vivid, horrible dreams. I've always – I passed the physical tests at the Academy with flying colors."

The woman rose from the chair, her right arm still cradled over her stomach as her left arm fell back to her side. She wasn't moving quite as gingerly as before, but her steps were still slow and methodic.

"Then tonight…I'm tailing a suspect, and next thing I know, I'm cornered in an alley by two…" She shook her head. "Bumpy foreheads. Yellow eyes. Fangs. Stench of death so strong I gagged. I work Homicide; that smell hasn't turned my stomach in years."

Angel nodded. "Miss…"

"The strangest part?" The woman shook her head. "As strong as they were, I handled them. I kicked ass. Then they…" Her brow scrunched in confusion and disgust. "…exploded."

"Miss…"

"Detective," she clarified. "Detective Beckett."

"Detective…" Angel rose from his own chair, coming out from behind his desk before leaning against the edge of it. He carefully watched the woman as she paced back and forth, the limp she came in with almost completely gone. "I think I know what you are."

"Okay." Kate shrugged. "How bad is it?"

"It's…not bad at all." A sideways grin tickled Angel's ageless features. "You're a Slayer."

Her eyes widened. "A what, now?!"

"These dreams…women fighting monsters? The world ending? That sort of thing?" When the woman nodded, chewing on her lower lip, Angel stood and crossed to the bookshelf by the windows. "They're not dreams so much as visions. What you're seeing are the battles of other Slayers, past and present."

"So I'm not the only one."

"No, you're lucky." Angel grabbed a book off the shelf, a heavy volume with a leather spine that had been caked in dust. "Time was, we only had one Slayer in the world. Thankfully, that notion's rather…antiquated."

Kate took the book with a frown, surprised at how heavy it was. "How many are there?"

"We don't know. But I'm pretty certain you're one of them."

"Wow…" Kate's eyes took in the ornate text in the book, the pages yellowed with age and frayed from years of use. She shook her head, her eyes not truly taking in the words on the page. She always prided herself on logic, taking what was in front of her and using that – and only that – to reach her conclusions.

It had served her well to the point where she had one of the NYPD's highest closure rates. It served her well in life in general, but despite all of the evidence in front of her, Kate couldn't bring herself to truly believe this.

Kate Beckett, superpowered monster hunter?

Yeah, right.

"I understand this is a lot to take in," Angel said, handing Kate a business card. "If you have any more questions, or you just wanna talk, feel free to call me. I kinda specialize in this sort of thing."

Kate took the business card, reading the top of it. "Angel Investigations." Her hazel eyes glanced at the logo on the side of the card, her head cocking to the side. "Oh, this is nice. Pretty little…" Her brow furrowed. "…bird?"

Angel blinked and sighed. "That's…not a bird."

Present day…

"I need to find her," Castle argued.

"Why?"

"To thank her for saving my life." Castle shrugged. "To give her back her weapon. Can't very well stake any vampires without a stake, now can she?"

"There's more than one way to kill a vampire," Angel said with a shrug. "Stake to the heart, fire, beheading…not garlic, though. That's a myth."

Grabbing one of the business cards off the holder on his desk, Angel flipped it over to the back before jotting some information onto the card. He slid the card across the desk Castle's way before sinking back in his chair, seeing something in the writer's eyes that told him this was about more than just giving Kate back her stake.

"She works Homicide," the vampire explained. "At the Twelfth. But you didn't hear that from me."

Castle pocketed the card and the stake with an impish grin before rising from his chair. "Thanks."

"Oh, and Mr. Castle?"

Castle stopped with a frown, wondering how the pale man seated at his desk knew who he was; he hadn't introduced himself. But as he turned to regard Angel again, Castle glanced at the bookshelf, immediately finding three of his books stacked on top of each other, Unholy Storm at the top.

Ah, so that was how it was – the PI was a fan.

"Kate Beckett's not a tree I would go barking up," Castle warned with a smirk.

Castle cocked his head to the side. "And why's that? Cause of you?"

"No." Angel scoffed and shook his head. "You could write a book about how disastrous my relationships are. It's just…Beckett's a hard nut to crack. Not to mention the Slayer thing. You're better off just going back to your one-night stands. She won't be one of your conquests."

Castle smirked. "What if I wanna be one of hers?"

"Good night, Mr. Castle."