Disclaimer: No I do not own Castle, but if I did...

A/N: I come bearing fic for you guys. I know many of you wanted another chapter, or follow up of the previous fic, but i decided to leave that as a one shot. It leaves the result open for the reader to decide what they think or want to heppen. Anyway. this thought occured to me after I rewatched the Pilot episode for the series (Sorry the names escapes me now) when Castle gave Kate an advanced copy of his book and then kissed her on her cheek. Also in this fic Josh does not exist - even in thought... LOL. Well enough from me, read and review guys.

In Theory

It was already way past working hours when Rick Castle casually strolled back into the precinct, bearing two tall cups of ninety eight percent fat free frozen cappuccino mochas. Castle was thankful for the air conditioning system that was keeping the building cool, a vast difference from the humid heat of the outdoors, even at this time of the evening. He was almost sure Detective Beckett would pull her face and wrinkle her nose at the sight of the drink, but he had brought it for her nonetheless. Besides, how she could handle drinking hot coffee in the middle of summer was beyond him.

The author frowned when he did not find Detective Beckett at her desk and his first action was to ask Ryan and Esposito where she was.

"She was in the interview room last I saw her," Ryan offered and Castle nodded his head in acknowledgement as he made his way to the interview room, unaware of the two male detectives gazes trained on him.

Two seconds later though, the terrible twosome decided to see just what was up with Beckett and Castle and followed the writer's footsteps, only they walked into the observation room and not the interview room. Esposito had already texted Lanie on what they thought was going and she arrived faster than they thought possible. Seeing his best team scurrying to the observation room, Captain Montgomery was surprised to see Castle and Becket on the other side of the glass – with no suspect.

Rick Castle came to a halt at the door and stood for a few seconds just watching his female pseudo partner as she examined a sheet of paper. Castle could see the cogs in her brain turning and he thought she was on to something, but a few seconds later she dropped the page to the table and sighed irritably. He stepped into the room and walked to where she was still standing, hands on her hips.

"Brought you some leftover dessert," he said and offered her the frozen mocha.

His statement garnered the reaction he was looking for and her eyes flashed dangerously, but she took the Mocha anyway, and refrained from asking him about his current flavour of the week. Just as he had expected she had pulled her face and wrinkled her nose at the drink, but took a long sip. And she had to admit, it was what she didn't know she wanted. Castle watched as she sipped from the straw.

He watched as her lips closed around the thin plastic, the way her throat moved as she swallowed and found that as hard as he tried, he could not get himself to look away. Castle shook his head slightly, as though the action would rid him of the images his brain had just captured and no doubt filed for long term memory.

"The interview was over hours ago, what are you still doing here?" he asked her when he saw her questioning gaze directed at him.

"I don't know. There's something odd about this mark," she picked up the gloss print she had been looking at earlier and handed it to him.

He closed the distance between them and took the six by nine print from her hand, looked at it closely and then rotated the page, trying to see if he had missed something. But, he knew he would not find anything, because while he was looking at the print, his mind was focused on the woman standing next to him. He knew she should not have stepped into her personal space but he had, and now her scent was invading his nose. He could not actually make out the specific smell, but it was calming, something that was uniquely Kate Beckett. No it was intoxicating…

Castle breathed in deeply and waited for his head to clear a bit before he opened them again. When he did however, he realised Kate had changed position slightly and that now instead of standing parallel to her, she was facing him at a slight angle. The first thing he noticed was that if he had to move his hand holding the photo half an inch to the left, he would be touching her inappropriately, he could see it from the thin shirt she had worn. Could it have been the cold temperature of the air conditioning that had caused that effect on her, or was it because of his proximity – he wondered.

She had opened an extra button on her shirt, dur to the heat in the building and as a result Castle could see a black lace bra against her pale white skin. Oh God, he was so sure if she knew what he was thinking she would have already pulled his ear or nose away from her, but thankfully for him, she obviously had no idea. She was still too focused on the picture he held.

Kate tensed slightly when she felt Castle close the distance between them. Sure, he had done this many times without giving it a second thought; that was just the way it was between them, but after that little comment about him being cute at the bar, she began to worry about how he would react to her. She felt his chest brush against her shoulder and she could not help the way her eyes fluttered closed at even the slightest of contact with this man. This annoying, infuriating, good looking, attractive man. He was driving her insane without even trying. She saw his lips moving and a few seconds later they stopped and he was looking at her expectantly.

Shit he had just asked her something and was clearly waiting for an answer, but she had none, seeing as she hadn't been listening to what he was saying.

"I'm sorry, what?" she asked.

"I said it looks like a bite mark."

"Yes Castle, I know it's a bite mark on the neck, my initial question was, how did our perp manage to get it at that angle?" She asked and then saw his sparkle the way they usually did when he was coming up with a theory. One she knew would eventually lead to no good.

"Whatever it is your brain is coming up with, I can guarantee you its not," she shot him down before he could even say anything.

"Awww come on KB, its just a theory," he whined and Kate knew she had to give in before he really started to annoy her. She took his mocha from his hand and placed his as well as hers on the table before she turned to face him, giving him the sign to go on.

"Okay, so our perp was stronger and taller than the victim," he started, "so he would be the one in control, and I would be the one playing him".

"I think I would have backed you up to the wall," he gently pushed Kate backward until her back came into contact with the cool glass window.

"Once you've got me pressed up against the wall, I have no place to move, leaving you hands free. Your hands would be on my hips," she said and Castle placed his hands on her hips hoping she would not move them, but Kate Beckett had no qualms with his action.

"And your hands would be around my neck," Castle continued, but stopped breaking that train of thought and coming up with another one, "no it would only be around my neck if you knew me intimately." He smiled at her his blue eyes dancing with mirth "If you didn't, then your hands would be on my chest, trying to push me away," at this statement Kate placed her hands flat onto Castle's chest. Castle wondered if she could feel his heart thundering beneath his rib cage, threatening to burst out of his chest cavity.

"You would be as close to me as you can possibly get," Kate whispered, and Castle took the hint. He pressed his body flush against hers and judging from the blush that crept up her neck and face, Kate was away how just how much he was affected my this whole thing.

"And that's when I would…" Castle broke off mid sentence, not knowing whether she would actually allow him to continue with this theory

"Bite me" she whispered so softly he almost missed it – ALMOST

Castle didn't need to be told twice as he slowly placed his mouth against her neck, before slowly moving to the position it was it the picture. Kate threw her head back and it hit the glass with such a force that it vibrated, causing people to look in their direction and the four patrons who were watching the exchange to jump back in fright. Luckily they could not see much. Her eyes closed automatically as a result of Castle's mouth on her skin and she had to fight hard to keep the desire filled moan inside. The She waited for the pain to come when Castle would eventually bite her, but she didn't feel a thing.

Castle gently nipped at the skin on her neck and ran his tongue soothingly over the spot, making sure he had not caused her any pain. When he was almost sure she would have a mark on her neck, Castle stepped back and admired his handiwork. It took Kate a few minutes longer to regain her bearings, and once she had, the Katherine Beckett that had escaped in the last few minutes had been put away and Detective Beckett was now in charge.

She walked over to the table, retrieved the photograph and walked back to the one way mirror from this side of the room. She lifted the six by nine gloss print and held near the mark Castle had just created on her neck.

"Castle," she growled, "that mark looks nothing like the one in this picture. Your theory proved nothing – I don't know why I listened to you in the first place,"

"My theory might be wrong Detective Beckett, but you certainly had fun trying to prove it," he shot back and Kate found she had no reply to that.

In the next room, Captain Montgomery stood, now three hundred dollars richer.

I hope you guys liked it. All spelling errors belong to me. I have read it over and made a few changes, but mistakes do happen.
I am also looking for a Castle beta, since mine mostly watches House MD, Jag and NCIS. LOL
Thanks and have a great week
Don't forget to leave feedback on your way out (",)
PSYCH