A/N: I had a very clear idea of how I wanted this to be and where it would go. Then the characters hijacked it, took it to a completely different direction and it became a monster that would never end. But I am determined to put it back on track and finish it how I wanted to, but it got way too long. So I am posting the first part now and hopefully the second part will be up tomorrow night.

Hope you guys like it.

Disclaimer: Castle is not mine. Unfortunately.



Kate Beckett pushed herself off of the desk she had been seating on for the past hour, staring at the murder board, and started in the direction of the break room for a much needed cup of coffee. She heard Castle sigh and stalk after her immediately, a small smile tugging her lips up. His idea was good, but it also had the potential to be terrible at the same time. Opening the door to the break room, she bee lined for the espresso machine and poured herself a healthy dose of cappuccino.

"You know it's a good idea, Kate. We can actually get this guy red handed." He insisted and she knew he was right.

She heard him close the door and felt his presence when he stopped just inches behind her. Taking a deep breath to calm her pounding heart at his proximity, she turned around and found him closer than she had expected. She almost hit him with her coffee mug accidentally and an almost inaudible gasp escaped her lips when she found his body so close to hers. He clearly had lost all respect for her personal space.

"Gates is not going to like it." She said quietly and took a sip from her cappuccino, trying to put some kind of distance between them, but he still didn't step back. He just looked at her, eyebrow raised, until she sighed, running a hand through her hair. "I don't even know if I have a costume, Castle. And besides, how are we even getting tickets to this thing? It's tonight."

"Don't worry about tickets. I was actually invited, but wasn't planning on going. But now, we have the perfect cover to catch our guy." He pushed back behind her ear a strand of hair that had fallen on her eyes. "Come on. Undercover mission. It's going to be fun." He grinned at her expectantly and she bit her lip, trying to prevent a smile and failing spectacularly.

"Alright. We have to run it by Gates first, though." She warned and he shrugged nonchalantly.

"She already hates me, anyway." He said and Kate narrowed her eyes at him.

"Which is why I'm doing the talking, Castle. We don't need to give her any more ammo to kick you out permanently."

"I'll be a very good boy." He promised with an innocent look and she rolled her eyes.

"Somehow I doubt that."

Gates grudgingly gave permission for their undercover mission at the famous Circus of the Damned Halloween party. The manager of the place was their prime suspect for murdering three young women in the past five weeks. After a lot of work, they had managed to narrow their suspect list down to Nicholas Hayes and they knew he would be at the party tonight, giving them ample opportunity to finally bring him in for questioning.

Kate left the precinct trying to figure out just what she could dress up as and how she would be able to get a costume at such short notice. She and Castle had parted ways at the precinct's doors and she drove home with a strong feeling that this was a really, really bad idea. They wouldn't be posing as a couple per se, but she knew they would have to at least pretend to be enjoying the party for appearance's sake. That meant dancing, maybe. Together.

This was such a bad idea.

Not that she thought Castle would try anything. He had been amazing these past couple of months after she returned to work and she was sure he would be a complete gentleman tonight. It was herself that she didn't trust. As much as she had tried to convince herself that she needed to solve her mother's murder before diving into a relationship with him, it was getting harder and harder to resist that magnetic pull she felt with him. She knew he loved her and she also knew that he suspected that she remembered everything. He had been asking her lately in his own subtle way and she was getting worse and worse at evading his questions every time he asked something. Going with him to a party tonight – undercover mission or not – it was going to be a real test to her abilities of resisting temptation.

With a sigh, she parked her car in front of her building and went up to her apartment. After taking a nice long, hot shower – it was already pretty chilly in New York as November approached – she opened her closet and tried to find something suitable for tonight. An hour later, she sat down on her bed, frustrated. She had nothing she could use as a Halloween costume. In fact, she couldn't even remember the last time she had actually dressed up for Halloween since she was usually working every year.

Lying back on her bed, she closed her eyes for a moment. There had to be something she could wear. When her phone rang a few minutes later, she jumped, startled, and reached out to where she had tossed it earlier on the bed.

"Beckett." She answered tiredly, not even bothering to look at the caller's ID.

"Found a costume yet?" Castle's voice greeted her ear and she smiled involuntarily.

"No. I have nothing that could pass as a decent Halloween costume. How sad is that?"

"Well, thank God you have me to save you then." He joked and she could hear his smile through the phone. "I think Mother may have something you can borrow."

"Really? What is it?" She sat up in bed, curious.

"Well, she has lots of costumes, but there's one that I think would look great on you." He said softly and she bit her lip, thrown for a loop by his sudden change of tone. She had been sure an innuendo was coming when he mentioned he had a costume for her. "Why don't you come over? You can try it on and if you don't like it, you can look through her things here.

"And she won't mind?" she asked unsure.

"Not at all, Kate. She was the one who suggested it, actually."

"Alright, I'll be there in twenty." She stood up, looking around for her shoes, slipping them on expertly.

"See you then." He said warmly and hung up.

Well, that was one problem out of the way, she thought, grabbing her purse, coat and keys on her way out. Twenty minutes later, she was parking near Castle's building. Getting out of the car, she braved the freezing wind and walked the remaining block. The warmth of the lobby of his building was delicious as she waited for the elevator. She rubbed her hands together, trying to warm them up as she cursed herself for forgetting her gloves in the car. Soon she was knocking on his door and was greeted by a smiling Castle. She smiled back and tucked her hair behind her ear, feeling suddenly self-conscious. He ushered her in and closed the door behind them.

"Come on, it's right here."

He led her to the living room, a hand resting comfortably at the small of her back, causing the butterflies in her stomach to come back to life. Draped over the back of the couch was a golden fabric and when he picked it up and held it up for her, she marveled at how beautiful it was. It was a dress and it was made of the softest fabric she had ever touched.

"It's beautiful, Castle." She breathed, taking the dress from his hands and holding it out in front of her for a closer look. "What's it supposed to be, though?"

"A Greek Goddess." He smiled at her and reached behind him. "It comes with these too, but you don't have to wear them if you don't want to." He handed her a head piece that looked like a tiara with golden leaves and a golden cape made of a nearly translucid material. "You could go as a Muse. Kind of." He suggested hesitantly and she smiled, amused.

"It looks perfect. Let me just go try it on." She took the other items from his hands and started to make her way to the downstairs bathroom. She hadn't gone very far when his hand stopped her.

"You can use my bathroom. There's a bigger mirror there." He offered and she bit her lip, nodding. "Come on."

He led her through his office and she could see the door to his bedroom slightly open. In all the years she had known him, she had never even peeked into his room and now that he was leading her to it, she felt nervous for some unfathomable reason. He opened the door to reveal a very big room – she was sure she could fit almost her entire apartment in there – with a large window overviewing the New York City skyline. The view was gorgeous, she thought, pausing to admire the sun setting. She could definitely get used to a place like this.

"You can admire the view later, Kate. Go try it on." His voice startled her out of her thoughts as his hand gently caressed her hip to get her attention. "I'll wait here." She looked up at him and found him smiling at her and found herself leaning back into him involuntarily, their gazes locking.

"So bossy." She shook her head with a teasing grin a few seconds later, trying to dispel the moment. She had to pull herself together. They hadn't even gone to this party yet and she felt like she was already fighting a losing battle.

Making her way to his bathroom, she closed the door behind herself and took a moment to admire the sheer awesomeness of his bathtub. It could easily fit at least six people and it had a lot of buttons that she was sure could do all sorts of amazing things. With a longing look at the bathtub of her dreams, she took her clothes off and put the dress on. Turning around, she looked at her reflection in the floor length mirror. She looked good. The dress stopped at her mid-thigh and showed her cleavage nicely without being slutty or trashy. It showed off her curves – she had finally put on some weight after losing more than a few pounds during her recovery – and it looked like it had been made for her. It was beautiful.

When had Martha worn this, she thought to herself, twirling in front of the mirror. Grabbing the head piece, she adjusted it on her head and looked at her reflection again.

"Kate?" His voice interrupted her thoughts. "Did it fit? Can I see?" He asked and she could hear the excitement and curiosity in his tone. Opening the door, she stood in front of him as he stared at her, first in shock and then hungrily, as desire shone in his eyes. Kate bit her lip, trying to quench her own desire for him.

"What do you think?" She asked self-consciously, shifting her weight from one foot to another.

"You look… Wow." She watched as he swallowed hard and rubbed a hand over his face. "You look like a goddess, Kate."

"Thanks." She said sheepishly. "Help me put the cape on? I think you can attach it to the dress." She handed him the cape and turned around. He carefully attached it to the golden metallic rings on each shoulder, his fingers dancing over her skin. Kate fought hard to prevent a shiver, but couldn't fight it when his lips touched her shoulder briefly. Biting her lip again, she decided to ignore his small slip and took a deep breath before turning around to face him. "What do you think? Should I keep it or lose it? The cape, I mean."

"Keep it. Definitely keep it." He said vehemently. "Unless you think it's going to get in the way." She shook her head and he smiled. "Then keep it. You look gorgeous." He said softly and she smiled at him.

"What are you dressing up as?" she asked curiously and he grinned at her.

"James Bond." He said with a wicked smirk and she laughed.

"Very fitting, Castle." She shook her head, amused.

"I thought so." He told her with a wink. "We still have some time to kill before show time. Maybe we could have dinner or something?" He offered and she nodded.

"Sure. Let me just change out of this first and I'll be right out." She said and grabbed his hand as he was turning to leave the room, making him look back at her, surprised. "And, Castle? Thanks for the costume." The smile he sent her way lit up the room and he stepped into her personal space again, leaning in to place a lingering kiss on her cheek, dangerously close to her mouth.

"My pleasure, Kate." He whispered and she closed her eyes, trying to breathe as normally as she could. When she opened them again, he was already gone.

"Don't you think the Ferrari is a bit too much?" Kate asked when he turned the alarm off and opened the door for her.

"We're going undercover. There's no rule saying we can't go all out with it and have a little fun." He winked at her and settled behind the wheel. "Plus, you're letting me drive. There's no way I'm going to miss this opportunity." He started the car and she chuckled.

"You're a child." She teased and he shrugged. "Come on, Mr. Bond. Let's get this guy."

He pulled the car into traffic and Kate allowed herself to sit back and relax. Turning to him, she took the time to just watch him, as it was something she didn't get to do very often. He looked incredibly handsome dressed as old school James Bond with a white tuxedo jacket and black bowtie and pants. His hair was brushed back with a touch of gel to keep it in place.

Yes, very handsome indeed, she thought to herself, pleased.

"What?" He asked when they stopped at a red light a block away from the club they were going to. She blinked and felt herself blush slightly. "You're staring at me. What is it?" He insisted and she shook her head.

"Nothing, you just look good, that's all." She admitted and could have sworn she saw him puff his chest out proudly at her compliment.

"Why, thank you, Detective. You look… well, gorgeous doesn't even begin to cover it." He said with a smile and she returned in kind, their spell only breaking when a car honked behind them. "Let's get this show on the road."

Castle parked the Ferrari near the club and locked it after they got out, engaging the sophisticated alarm system the car had. When he offered his arm to her, she looped hers through his without hesitation and they made their way to the front of the line, where Castle handed the security guy their VIP tickets, much to the dismay of the people waiting in line to get in. Once inside, they left their coats with the hostess and Kate took his hand, pulling into the already crowded room. The place was amazingly decorated for the occasion, giving off that creepy Halloween vibe with the lights, music and pictures displayed on the walls. Kate knew there were four floors in which the party happened and thought they could mingle and scout the locations for the next hour.

"So what's the plan?" His voice in her ear took her by surprise and she jumped, startled, her back hitting his chest. They were making their way through the crowded dance floor and Kate found herself being pushed further back into his chest. Taking a deep, steadying breath, she turned her head to the side.

"Let's just take a look around for now." She managed to say and found his lips dangerously close to hers. Swallowing hard, she turned away and braved her way through the crowd until they reached the bar.

"Do you want a drink?" He asked when they finally made it to the bar, his hand making its way to her hip.

She looked down at where he was touching her and smiled, amused, that he was staking his claim on her. She had seen a lot of guys checking her out on their way in and it was incredibly amusing – and sweet – that he wanted to keep the men away from her. It was funny, really, how much she had changed since she had met Castle four years ago. Had this happened back then, she would have immediately slapped his hand away; now she allowed herself to enjoy his touch (not that she would tell him that, obviously). Of course, back then she thought he was a pain the ass, as opposed to now, that she was in love with the guy.

"I'm on duty, Castle." She turned around to look at him and he nodded, already signaling the bartender.

"Two Cokes, please." He ordered and slipped the guy a ten dollar bill. The young bartender returned with their beverages and she watched as he smiled at the kid. "Thanks, man. Keep the change." He handed her a glass of Coke and held his out for a toast. "To a successful mission." He grinned and clinked his glass to hers.

"To a successful mission." She repeated with a smile and took a sip. "We should find out where his office is. See if he picks his victims in advance." She said quietly and he nodded. "Keep your eyes out for him."

"Got it." He acquiesced and leaned back against the bar. Kate did the same and they stood there, arms touching, watching the crowd of dancers in the most varied and outrageous costumes. From time to time, they whispered to each other about a particularly funny costume, but after an hour, they still hadn't seen any sign of their suspect. "Maybe we should move to the dance floor. He might be somewhere in there and we just can't see him from here." He suggested and Kate bit her lip. With a sigh, she agreed, not having any better ideas herself. "Alright, come on." She looked at his extended hand warily and he sighed. "I'll be a perfect gentleman, Kate. You know that." He promised her and she bit her lip again, but took his hand nonetheless.

She knew he would be a perfect gentleman. That wasn't the problem. It was herself she didn't trust tonight. Nevertheless, she led him to the dance floor and through the crowd, until she found a spot that would fit them both. Stopping abruptly, she felt him bump into her back, almost making her lose her balance. His arm immediately grabbed her around the waist before she could fall and pulled her back against him. She closed her eyes at the sudden contact and breathed heavily through her nose.

"Keep your eyes out for him." He repeated her words in her ear, his lips brushing against her skin, and she opened her eyes, trying to get her breathing under control.

Sweet Jesus, what was he doing to her?

He kept his arm around her waist, holding her close and moving his body to the beat of the song playing. Kate tried to ignore her racing heart and the way his body moved with hers and focused on locating their guy. After a few minutes, however, they still had nothing, so she decided to turn around to take a look at the other side of the room. With her heels, she was almost as tall as he was and could easily see over his shoulder. It also put her face to face with him, which proved to be a huge mistake. Their gazes met and locked and she found she just couldn't make herself look away. After a few seconds, in which Castle had pulled her even closer, Kate managed to tear her eyes away from his, only to have them stray to his lips, then back up.

This was a terrible, terrible idea.

She couldn't keep her eyes away from his as she watched him lean in slowly, giving her time to change her mind, but she just couldn't make herself move. Not when his arms were wrapped firmly around her waist and their bodies were pressed together like that. She couldn't even think, let alone make the coherent, sensible decision of stopping this. When his lips brushed against hers, she sucked in a gasp, making him pull away. Like a magnet, however, her lips followed his and she closed the distance between them again, firmly pressing her lips to his. He seemed surprised at first, but soon started moving his lips with hers and Kate lost herself in the kiss for a moment. His tongue caressed her bottom lip and she granted him permission for it to come in and dance with hers. When their tongues touched, she almost felt like she had been deliciously zapped and had spontaneously combusted at the same time as a moan escaped her lips. He pressed her ever tighter against his body and groaned against her mouth.

Kate couldn't think straight when he finally pulled away and started a trail of wet kisses on her neck, sucking on her pulse point. She was breathing heavily and her desire for him had risen exponentially. Throwing her head back and giving him more access, she sighed contently at his tongue on her skin and the feel of his body pressed so intimately against hers. He was taking his sweet time exploring her neck and it was slowly driving her crazy.

It took someone bumping into them a little harder when a crowd favorite song started to play to make her snap out of the trance she was in. Opening her eyes suddenly, she gasped when he found her lips again, pulling her under for a few seconds longer as his tongue did delicious things to hers. It took all of her self restraint and control to pull away from him.

"Wait." Her breathing was coming out in gasps and the look in his eyes almost made her throw caution to the wind ravish him right then and there. "Castle, we can't do this now." She leaned heavily against him and was thankful that his arms were still holding her up, otherwise her knees would have given out already. He touched her cheek, his thumb caressing her skin softly as he leaned his forehead against hers.

"Right. Undercover mission. Find serial killer. Focus." He said and she smiled at his ragged breathing, proud of herself for doing this to him. "Got it." He finished, but still kept her firmly pressed against him. "Do we have to?" He added after a minute and she laughed.

"Yes, we do." She told him with a smile and leaned in, pressing her lips against his again. "We can continue this later." She kissed his surprised look away and laughed when he all but growled against her lips.

"I am definitely holding you to that." He kissed her neck, but she pushed him away. "What?"

"I see him. Ten o'clock." She told him over the loud music and he nodded, leading her in the suspect's direction.

A/N: Thoughts?