AN: So, I've written this one on a whim, really. I realized I'd never taken part in this annual event, and not knowing when a thing might end up being one's final thing, well, I didn't want to miss out on the opportunity. Searching for Halloween prompts on the interweb, I stumbled upon one about a couple that wasn't yet a couple, a couples costume, and love. After that, I couldn't get our two as the two I have them portray in this piece out of my head. How sexy they would've been.

Chapter 1

En route back to her desk that early morning, Kate turned the corner at the far end of the bullpen and found Rick and the boys huddled around her desk, giggling and exchanging high fives. In and of itself, it wasn't a scene out of the ordinary. She'd grown accustomed to the musketeers and their bromance, and to the antics it spawned.

That wasn't the first time she'd walked in on them engaged in such a boisterous confab over the past couple of days, though, and when they spotted her approaching and Javi's eyes hit her with a brazen head-to-toe sweep, it was clear something was going on, and that whatever it was, she'd been unknowingly roped into it.

"I don't know what the hell you're looking at me like that for, Espo, but I do know you should cut it out." She gladly accepted her customary morning cup of coffee from Rick's outstretched hand, brought it to her nose, and inhaled the sweet hint of vanilla. "What are you girls cackling about over here, anyway? By how pleased you seem to be with yourselves, a person might think maybe one of you got lucky last night. Personally, I don't like wasting my time on wild theories. That's Castle's neighborhood."

Rick scrunched up his face, despite the truth of it, and the three men carved a path, let her pass and settle behind the desk.

"Guess you didn't either," Javi bit back. "Grump." He caught the subsequent glance passed between Kate and Rick, dove headfirst into it like a kid into a wave. "Maybe the two of you could finally get on with it and help each other out with that. Just sayin'." His partner's eyes widened as he labored to hold in a burst of laughter. "Good luck, Castle," he said walking off. "If the grump goes for it, I'll show up this weekend as Bo Peep, and Ryan'll come as my sheep."

Kevin's head whipped around. "What? How the hell…" Grousing under his breath, he chased off after Javi, leaving Rick and Kate alone.

Rick dropped into his seat beside her desk, sipped from his morning blend in preparation. "Did you notice the-" He pointed with delight at her cup, at the bright orange pumpkin drawn across its curve in marker. "They let me do it while I was waiting in line. Nice touch, huh?"

Halloween was only a few days away. What more appropriate a time to be afraid of something, Kate thought, even if the fear stemmed only from the idea of asking him what the hell was going on. Honestly, she probably didn't really want to know, but, as she so often seemed to where he was concerned, she caved to curiosity.

"What do you want, Castle? It'll save me time and you the pain of trying to be cute if you just tell me."

A smug smile tugged at the corner of his mouth. "I assume the implication is that my cuteness usually comes naturally."

"Of course you do," Kate replied with a roll of her eyes. "Spill it."

Rick set his cup on the desk and dug into his jacket pocket, pulled out a folded square of paper. "Okay, well, you know, of course, Halloween is this weekend, as is my annual celebratory bash. Please, Katherine, this is a place of business. Try to contain your excitement," he cracked when her expression didn't shift an iota.

She gave him the side-eye, let it linger.

"I know this is last minute," he said as he opened the paper full, "and you probably already have a costume planned, as I did, but I came across this photo last night and I instantly thought of us, and I was hoping you might consider doing a… couples thing with me, instead."

Couple.

Even employed in innocent context the word sparked a flutter of Kate's heart. And it hadn't gone unnoticed that he'd wielded it gingerly, either, but, given where they currently were in their evolving relationship-or where he thought they were-that came as little surprise.

"Castle, I never said I was going to your party, first of all, and, second of all, we aren't a couple."

A paper cut across her fingertip was what the wait to have him felt like, one that never healed and throbbed whenever it was touched, and hearing those words out of her own mouth made it sting and burn.

"Yeah, because that's a reminder I need," he mumbled as he handed over the printout. "Look, you say you don't know if you'll be there and then you always show up. I just thought it might be fun if you showed up wearing that. Come on, Beckett, it's simple. You have the long hair now, not to mention the eyebrows and the sarcasm. You're practically her already."

Kate scrutinized the picture. It really would be simple, and she still had absolutely no idea what she was going to wear when she inevitably did show up. Lanie had suggested she don skintight pants and cherry-red lipstick and come as Sandy from Grease. Like that was going to happen, and certainly not now, after the way Javi had already been gawking at her.

"You probably should've started trying to grow the moustache as soon as last year's party was over, Castle," she teased. "It might've been ready by now."

He pushed back in the chair, unamused. "Oh, so you were planning on dressing up as a comedian then. I guess that would've been one way to guarantee you'd go unrecognized." Out of nowhere, he slapped his hand down on the desk. "Do this with me, please. I'll handle everything. My mother has a theater friend who said she'd help out with the clothes, not that it requires all that much, which is really the second best thing about it."

She slid the visual aid back his way, curled her fingers around her coffee. "What's the first?" she asked, noted his hesitation.

"That it's… something we can do together, obviously."

"You wanted to say Espo in a dress," she accused with narrowed eyes, and Rick appeared just as guilty as he, in fact, was. "That actually might just make it worth it."

xxxx

For being necessarily clothed in a costume-an enterprise that, year after year, proved aggravating above all else-Kate felt surprisingly comfortable. She'd even opted for the subway over a cab, given more looks than she'd received in a car crowded with a garish assortment of characters, and earned herself a correct first guess as to whom she was portraying for the evening from the doorman at Rick's building. All in all, the night had kicked off as well as it could've, and she still had Javi's and Kevin's getups to look forward to.

She found the door to the loft cracked open when she stepped off the elevator, the distinct and silly chorus of "Monster Mash" seeping out into the hallway, which provoked a hint of a smile. It wouldn't be the only time she'd hear it played over the next several hours, she knew; in fact, she'd probably hate it again by the time the party was over, but it was perfectly Rick to not care how silly it was, and that was, after all, much the reason she was as she had been for so long: in love.

Inside, the majority of the crowd was gathered around the kitchen, making small talk with makeup still fresh and wigs in place, but it was on Rick that her eyes landed and fixed. He was standing away from the others with his phone to his ear, his free hand fidgeting with the chain of the pocket watch laced through the buttonhole of his lapel.

It should've made her want to laugh, the moustache he'd secured just slightly askew above his lip, but that wasn't her reaction, at all. As she stood there watching him, she thought back on earlier days and how he'd often chosen not to make use of a razor, how much she'd quietly taken pleasure in that, and how sexy it'd been to her. Those days were few and far between now, but the reminiscence had her instantly buzzed, and without having swallowed a sip of his self-lauded green party punch.

Not that Kate had minded, but several minutes passed before Rick finally noticed her there. When he did, his entire face lit up and he hurried straight over, quitting his call along the way.

"Morticia, cara mia," he said embodying his role, drinking in all that was to be his play wife for the festivities. "I knew you'd look incredible, Detective. I do so love being right, and that it happens so often."

She cocked her head in disapproval. "And you've hidden yourself pretty well in this whole Mr. Addams thing, Castle. Too bad your ego's still showing." He didn't flinch with the bite. He just continued to stare at her, his lips gently parted. "What's wrong with you? Why are you-?

All at once, he seemed to plug back in.

"No, there's nothing wrong. I'm just happy you're here, that's all." Part of him truly wondered whether or not she'd show, even with the added incentive of her partners' impending humiliation. "May I get you a wonderfully ghoulish drink to start?" He offered a hand in request of hers, pressed his lips when she gave it, as Morticia's ever-bewitched husband would do, and led her toward the kitchen.

Save for a few familiar faces from the precinct, Kate didn't recognize most of the people there, she realized with a brief scan of the room, and not only because their identities were masked behind others. "I know Lanie's on her way here. She texted me a little bit ago. Where are Ryan and Esposito?" The pair was set to be the real entertainment of the night.

Rick presented her with a cup of punch that had a plastic eyeball bobbing around in it, ladled another for himself. "Oh, yeah, I was talking to Ryan when I saw you were here. He called to say they were smooshed in the back of a cab in traffic with Jenny, and that he was very hot and very itchy in his sheep head. He didn't appreciate that I was amused by all of that. Cheers to my queen of darkness."

They tapped cups and each took a gulp, Kate's lips puckering with the sour taste. "Now I remember why I never drink this stuff at these parties. This is disgusting, Castle." Meanwhile, he'd swallowed down nearly his entire share, and he couldn't have looked happier about it. "Of course he likes it," she remarked to herself. "Do you have anything stronger than this? Something that maybe doesn't glow in the dark?"

He reached into his pocket and pulled out a prop cigar, bit it between his teeth for a couple of seconds before curling it away in his fingers. "You know, for this brilliant idea of mine being thrown together at the last minute, I just have to say you really are wearing the hell out of that dress, and for granting me the wish, I have anything you want."

All the years, all the parties, but something on that night felt different. Kate felt different.

It was supposed to happen. She'd learned to stop pushing back against that reality, and even to dream about what it would be like when it did. But it wasn't supposed to happen yet. There was her mother's case and Dr. Burke and a wall and healing to be done. There was a plan. She had a plan. But she'd barely walked into the loft that night, barely spent five minutes with Rick, when this urge had come over her, and the power of it scared her.

"Maybe just a beer for now, actually," she replied. "I don't want to end up like Ryan last year." They both chuckled with the memory, because they were able to recollect it. Kevin, they imagined, wouldn't be able to say the same. "I'll see how things go."

"I'd steal the moon and stars from the sky for you if I could, cara mia, and bathe us both in beautiful darkness." He bowed. "I am at your service, always."

Gomez Addams set off for the refrigerator in his pinstripes, without a clue as to how well she understood Richard Castle would steal them for her, too, if ever she asked.