So as a few people have pointed out Kate would have been with Josh at this point and Rick with Gina, and since I agree that neither would cheat let's say that those relationships had already run their course and that Rick and Kate were single in this episode.

What if, during their moment over the letters, Kate had kissed Rick.

Kate: Well, these are just love notes. There's nothing in here about the escape.
Rick: Well, then we have to look at these like a romance novel, not a murder mystery. These people are bearing their souls in these letters, and if we're lucky, we'll find our Saywatanayo. In the Shawshank Redemption, Andy was trying-
Kate: No, I know what it is. I'm a cop, I've seen the movie. It's just, there's nothing about that in here. The only thing that Amy talks about is being innocent of the crime she was convicted of and how much she misses Greg.
Rick: Yeah, it's pretty clear Greg misses her, too. Listen to this, "The days without you grow longer, but my love for you grows..."
Kate: Stronger?
Rick: "Harder." A poet he's not.
Kate: Yeah, well, not everyone is a bestselling crime novelist. And it doesn't mean that their love was any less. Listen to what she wrote to him, "I can't bear to see you suffer. Make a new life with someone else. Just be happy. If anyone deserves it, it's you."
Rick: I think I have his response to that. "I don't believe in much, but I believe in us." I like this guy.
Kate: Mm-hmm.
Rick: "And no matter the obstacles, no matter how hard you try, you'll never get rid of me. I love you.".

Kate felt her heart stop as he said those words. Logically, she knew he wasn't talking to her, he was just reading the words on the page in front of him, but the fact her heart was skipping a beat told her something that she wasn't entirely sure she was ready to know.

As she looked into his eyes, and he looked into hers, she felt herself lean forward as her eyes shut of their own accord. Her's eyes were open just long enough to see the surprise on Rick's face before she shut them tight and gently touched her lips to his.

He stayed still as a statue before she felt his hand on the back of her head and he pulled her in, deepening the kiss. Her hands travelled up to rest on his chest and she pushed him away. "Sorry," she said, pulling back to put some space between them, "I shouldn't have done that."

Rick looked hurt. "Kate," he started to say, his voice husky.

They were then interrupted by Ryan coming into the room. He looked at the two of them, who were still looking at each other and teased, "Am I interrupting something?"

Kate ignored his words and turned to face him. "What you got Ryan?"

He explained that he'd found something and Kate nodded along, but she was aware that Rick was still staring at her. She tried to ignore him as Ryan spoke but she could see the hurt and confusion on his face. Ryan then left the room, Kate telling him they were going to finish up with the letters before joining him and Esposito back out in the bullpen, and Kate turned back to look at Rick.

"Not now Castle," she said softly. The look of hurt and confusion stayed on his face and she sighed. "I'm sorry Rick, but we have a case."

"You're the one who kissed me, Kate," Rick said, keeping his voice low.

"I know," Kate answered. She still wasn't sure why she'd done it, but she had been the one to initiate it. "Look, can we talk about this later, please? We can't do this here."

"Sure," Rick said, leaning back in his seat.

Kate stared at him for a moment longer then shook her head and dived back into the love letters in front of them.

-/-

Once the case was over Kate knew that Rick would want to talk to her. She'd managed to avoid it on the night of what she was calling in her head 'the incident', but now that the case was over she knew she owed Rick a chat. And Rick knew it too. As she finished up Rick stared at her, even more intently than normal.

She wanted to tell him to knock it off, but she knew she owed him an explanation and he was being pretty patient about waiting for it. When all the paperwork was finished and sighed off she sighed and turned to Rick. "Are you busy tonight?" she asked.

Rick shook his head.

"Would you like to come back to my apartment so we can talk in private?" she asked him.

This time he nodded. Kate waited to see if he was going to say anything but he stayed silent, just continued to stare at her. She got to her feet and pulled on her jacket, Rick copying her motions.

"See you tomorrow," she said to Ryan and Esposito as the two of them walked past the partner's desk.

"See ya," Ryan called after them. He and Esposito had noticed that there was something different about the two of them today but hadn't put too much thought into it, they both found trying to work out what was going on between the writer and detective far too complicated sometimes.

The ride down in the elevator and then the ride from the precinct to Kate's apartment was done in near silence. Kate tried to start a conversation a few times but found herself unable to think of anything to talk about, so they both just stayed quiet.

Kate unlocked her front door and walked in, leaving the door open in invitation to Rick. He paused in the doorway but then followed her in as she took off her jacket and hung it up, before toeing off her shoes and leaving them by the door.

Rick stood in awkward silence, not really sure about what to do.

"Make yourself comfortable," Kate invited, "Do you want a drink?"

She was playing for time, trying to put off their chat, and Rick knew it. "I don't want a drink Beckett," he told her as he took off his jacket and threw it over the back to the sofa, "I want to talk."

Kate sighed but then nodded. She sat on the sofa and Rick sat on the other end. They both turned in their seats so they were looking at each other. Kate didn't know what to say, but she knew she had to start, she was after all the one who had kissed Rick, Rick hadn't been the one to close the gap between them, she had.

"So," she started but then stopped.

"So," Rick parroted, "You kissed me."

"I did," Kate accepted, "But I shouldn't have."

She expected Rick to make a comment but he stayed quiet, she was beginning to get a little concerned, he'd been quieter today than she had ever known him to be.

She brushed her hand through her hair. "I don't know what came over me," she explained, "But when we were reading through those letters I just wanted to kiss you, so I did."

"Why?" Rick asked.

Kate blinked a few times. "Like I said, I don't know," she answered.

"Then why avoid the subject?" Rick asked her, "You could have just apologised at the time and that would have been it. Yes, it might have made things weird for a bit but there's no feelings involved so we could have just laughed it off, eventually. You avoiding the subject makes me think there's more to it than you're letting on."

"I need a drink," Kate said, getting to her feet and heading to the kitchen. She poured two glasses of scotch and then brought them back to the sofa. She handed one to Rick then sat back in her recently vacated seat. She took a sip and then watched Rick as he did the same, watching as his adam's apple bobbed as he swallowed.

She bit her lip then ran her hand over her head, trying to collect her thoughts.

"Kate," Rick said, his voice so soft that Kate could barely hear it, "Do you regret kissing me?"

Kate thought for a moment. "Yes," she said honestly. She saw Rick's facial expression drop. "But not for the reason you think," she said quickly.

Rick frowned at her and took another drink. "Then why?" he asked.

"You remember how after the summer Lanie and the guys were pretty hostile towards you?" Kate asked.

Rick nodded, not really sure where this was going but willing to sit there and find out.

"Well they knew something you didn't," Kate told him, "I broke up with Demming before you left for the summer." She watched as partial understanding appeared on Rick's face. "And when I asked to talk to you I was going to ask if the offer to go to the Hamptons was still on the table, and then Gina showed up so I didn't."

"You were going to come with me?" Rick asked her.

Kate shrugged. "I'd realised that maybe a weekend with you wouldn't be too bad."

"Right," Rick said, "But what's that got to do with what happened yesterday?"

"When you came back I didn't want you around," Kate admitted, "You'd left with Gina, which was bad enough, but then you didn't call, you just dumped us, me." She rubbed her face again, this was a lot harder than she'd thought it would be, but she needed to talk. "But then, on that case, I remembered why I liked having you around so I let you come back."

"You let me?" Rick asked, "I won our bet."

Kate just raised an eyebrow.

"You let me think I'd won the bet so you could save face," Rick exclaimed.

Kate tapped the side of the nose. "Anyway, then you were back, and we got back into our groove, which I had missed over the summer, and it was fun." She took a drink, wetting her suddenly dry mouth. "And then when you were reading those letters, we just got so close and then I kissed you." She took another drink, playing for time, and she saw that Rick was also drinking. "I don't regret kissing you," she said, then to stop Rick from speaking she continued, "I just regret that I kissed you at the precinct." Her voice had dropped so low that it was barely audible.

It took Rick a minute to compute what she'd said. "So it's not the kiss but the location of the kiss that bothers you?"

"Yeah," Kate said with a shrug.

"Which means you wanted to kiss me before yesterday," Rick said, a teasing tone coming into his voice. Kate almost smiled, this was more like the Rick she'd come to know, but she lifted her glass to hide the slight quirk of her lips.

"Maybe," Kate said.

"So do you want to kiss me now?" Rick asked, moving closer to her.

Kate shrugged. "Does it matter Rick?" she asked.

"I think it does."

"You kissed me back," Kate pointed out.

"I did," Rick admitted.

He'd been slowly moving closer to her and now their faces were barely inches apart.

Barely breathing Kate blindly felt for her coffee table and put her glass down, not taking her eyes off Rick's face. Her eyes flicked between Rick's face and his lips, and she was aware that Rick was doing the same.

"So," Rick said in a soft voice.

Kate closed the gap between them and pressed her lips to his. Immediately she felt one of Rick's hands reach up and touch the back of her head, pulling him to her.

After a few seconds, Kate pulled away.

"Please don't say you shouldn't have done that," Rick said in a low voice.

Kate reached out and took the glass from his hand and placed it next to hers. "Oh no Rick, I definitely meant to do that this time."

Rick smiled at her and then pulled her back to him, his second hand wrapping around her body until it rested on her back. Her hands went up, one threading up into his hair while the other gripped his shirt and pulled him the remaining distance.

This time when their lips touched there was no questions, no hesitation, from either of them, there was just barely controlled passion.

Kate released her grip on Rick's shirt and started to try and unbutton it one-handed.

"Yeah," she whispered, pulling back to give her just enough room to speak, "Meant to do this."

Rick laughed and pulled her back to him.