A/N: Today's prompt comes from justlook3, and it's Castle – Never too old for Santa Claus.

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Never too old for Santa Claus

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"Why Detective Beckett, Christmas decorations. I'm surprised," Castle said as he waltzed into the precinct.

Beckett glanced up, eyes twinkling alongside the little light-up Christmas tree sitting on her desk. "It was a gift," she explained dryly. "Besides, it's not like I never put up Christmas decorations."

Castle grinned and handed her a coffee cup. "Not usually anything this overt though."

"What can I say?" she said lightly. "I guess I was feeling adventurous this year."

"I'm glad to hear it," Castle replied, his eyes twinkling as he watched her take a sip of her coffee.

She'd barely tasted it when Beckett was lowering the mug again. "Castle! What is this?" she demanded, obviously annoyed that he hadn't brought her usual.

"Peppermint-flavoured latté," Castle explained blithely.

"Wha…?"

"You just said you were feeling adventurous," he reminded her. "It's one of the new seasonal flavours."

"It's something alright," Beckett muttered, glaring at her cup.

"Oh, come on Beckett, get into the spirit of the holidays!" Castle said cheerfully.

She glanced significantly at her little tree.

He waved a hand at her. "Doesn't count. You didn't even buy it. Who did, by the way?"

She smiled. "Ryan, of course."

Castle chuckled, "Of course."

"What are you doing here today anyway," Beckett asked her. "We don't have a case."

"I can't just drop in?" he asked.

"You can," Beckett acknowledged. "But usually when you do, you have an ulterior motive of some kind."

"How well you know me," Castle replied. "I had an idea."

She pretended to look annoyed. "Oh no."

He ignored her. "I was wondering what your Christmas plans were."

Beckett faltered. "Umm… Well, I'll be spending the day with my Dad, why?"

"Because you are cordially invited to the Castle family's Christmas bash on the 23rd, conveniently timed before the day itself so that people spending the holidays with family can attend. There'll be everything Beckett, tinsel, lights, Christmas bows, mistletoe," he added waggling his eyebrows. "And who knows, the man in red himself might make an appearance."

"The devil's coming to your Christmas party?" she asked with a smirk.

"Not the devil," Castle corrected indulgently. "Santa Claus of course."

"Just what is the average age of your guests going to be, Castle?" Beckett asked skeptically.

"Mental or chronological?" he countered quickly.

She shook her head, "Never mind."

"What does age have to do with it?" Castle asked curiously, dropping into his chair.

"Don't you think you're getting a little old for Santa Claus?" she asked practically.

"Beckett!" Castle cried in something akin to horror. "Blasphemy. I never want to hear you say that again." Just then the rest of their team walked up. "Hey Ryan, Esposito, Christmas party on the 23rd, my place, you guys in?" he asked.

Esposito paused to consider the offer. "Yeah, I've got nothing that night, except for maybe some last minute Christmas shopping. I'm in."

Ryan nodded as well. "We're going to Jenny's parents on Christmas eve, so the 23rd should be fine. We'll be there."

"Dinner with the in-laws, huh?" Esposito asked his partner.

"Jenny's parents like me!" Ryan squeaked.

Esposito's smile turned evil, "Sure they do, bro."

"They do," Ryan insisted.

Castle and Esposito exchanged a look.

"Okay, her father always gives me an extremely firm handshake in greeting," Ryan admitted. "But ever since our engagement things have been a little less… What's the word?" Ryan trailed off.

"Threatening?" Esposito supplied.

"Terrifying?" Castle suggested.

"Yeah," Ryan conceded.

Beckett smirked.

"Well," Castle said after a moment. "I'm glad the two of you are free. Santa might have something special for both of you."

"Santa's coming to your party?" Esposito asked skeptically.

"I know, right?" Beckett replied.

"Cool!" Ryan said at the same time.

Castle beamed at Ryan and ignored the skeptecism of the other two detectives.

Esposito shook his head indulgently, deciding to try and enter into the spirit of things. "Yeah, you're right, guys. I guess it could be fun. And hey, who doesn't like presents?"

"Exactly," Castle replied.

All three men turned towards Beckett.

"Giving gifts to your guests is a lovely idea," she conceded. "I just think we're getting a little old for Santa Claus is all."

"Aw, you're never too old for Santa Clause," Castle told her firmly.

Esposito grinned. "Yeah, Beckett. Unless you were a bad girl this year."

That got Castle's attention.

She smirked. "Oh wouldn't you like to know."

"I definitely would," Castle told her, glancing at the guys.

Ryan and Esposito looked at each other.

"Yeah, me too," Esposito admitted.

"Definitely," Ryan agreed.

Beckett just smirked. "Alright guys, enough's enough. Can we please get back to actual work?"

"Fine," Esposito said petulantly. "We've got to head down to records anyway."

"See ya, Castle," Ryan added before walking away.

Castle didn't leave, settling down on his chair and staring pointedly at his partner.

"What?" she asked in amusement.

"What do you have against Santa Claus?" he asked. "Traumatic incident in your childhood? Unpleasant time on Santa's lap? Let me guess, you were one of those kids who stopped believing ridiculously early at about age eight."

She shook her head slowly. "The opposite actually," she murmured.

He looked surprised.

"I tried to keep believing longer than I probably really did," Beckett explained. "Didn't quite want to let it go."

"What made you?" Castle asked gently, leaning forward slightly.

"Well, something like that gets a little awkward in high school," she joked.

"Right."

"Yeah."

"I was eight," he admitted softly after a moment.

Beckett looked up in surprise. He was such a big kid; she'd always assumed he'd have dragged out his belief in things like Santa Claus as long as possible.

Castle shrugged. "My mother was in a touring production of A Christmas Carol that year. It's hard to hide Santa's presents in hotel rooms. I found them accidentally one day. Couldn't bring myself to tell her. "

She smiled at the consideration of that, even at eight.

"So why so gung ho about Santa now then?" Beckett wondered.

"Part of the magic of Christmas I guess," he explained. "People getting together, exchanging gifts. Besides, there's something about a gift from Santa Claus. It's different from a gift from a specific person. It's a gift given without expecting anything in return. I like it."

Geckett bit her lip. "I haven't done the big Christmas thing in a while."

He shifted closer to her. "You're never too old for Santa Claus, Beckett."

She tilted her head to the side briefly. "Unless you've been naughty," she smirked.

She watched his eyes warm in pleasure. "I'll put in a good word for you," he promised.

Beckett nodded and took another sip of her coffee, wincing when she tasted the flavoured latté.

"And I'll switch back to the usual tomorrow," Castle promised her.

"Thank you."

xxxxx

Castle was puttering around his apartment, absently tidying after his Christmas party.

It had been everything he'd hoped for. Lots of friends, family and fun. Everyone had seemed to have a good time, even the biggest skeptics, Esposito and Beckett. Ryan was a given. He'd arrived in a novelty Rudolph tie. Jenny clearly found it adorable. Everyone else found it hysterical. But even Beckett had warmed to the idea, at least enough to give him a kiss on the cheek under the mistletoe. Castle suspected he might have been able to finagle something more had they not been surrounded by her colleagues. But she'd liked her present, Christmas mittens, complete with string attaching them together so they wouldn't get lost.

He could tell the gift had surprised her. But she'd loved it, her little piece of a child's joy at Christmas.

Castle had known she would. That was the magic of Santa.

He smiled again, remember the look of pleased wonder in her eyes when she realized he'd gone understated and not expensive with the present. He loved surprising her. Besides, he knew her well enough now to know what she really liked.

Wandering over the mantelpiece Castle straightened the garlands that had been disturbed in the commotion. That was when he saw it, the small wrapped package.

Curious, he picked it up. It was a rectangular box, maybe ten inches long and a couple of inches wide, and wrapped in shiny red wrapping paper. That was when he saw the tag.

"Dear Castle," he read. "Merry Christmas, Love Santa." He flipped it over to read a message on the back. "I would tell you not to open this until Christmas, but I know better."

Grinning and taking that as tacit permission, Castle ripped into the package, gleefully. After all, there was only one person it could be from.

Inside was a pen.

He frowned. He didn't understand. It was a lovely pen of course, but somehow it wasn't… it wasn't what he'd been expecting. That was when he saw the card underneath it.

'Spy Equipment International," it read. "The following pen may appear to be nothing more than an ordinary pen, but look again. The top contains a flash-free camera for when the modern spy can't be seen, and the body unscrews to reveal a secret hiding spot. Perfect for passing covert messages."

Castle's face lit up in glee. He flipped the card over to read the message written in a very familiar scrawl. "You're so determined to see CIA involvement in everything that this seemed appropriate. Merry Christmas Castle, love Santa. P.S. You're lucky that you're apparently never too old for Santa Clause, because I bought this in a toy store, albeit a high end one."

If it was possible, Castle's smile widened. It seemed he really had spread the magic of Santa this year, and to her of all people. In the end, that was all he'd really wanted.

Curling up on his couch, the writer reached for his phone. "Good evening Detective. Sorry to bother you so late at night, but you'll never guess what I found next to my stocking…"

xxx

The end