I got this story idea when I heard a rumor that Kate might end up liking the Scotland Yard detective that she has to work with in 'Limey.' The idea made me so mad that I had to do something about it, in fan fic, at least. This was all before '47 Seconds' aired, so instead of being an AU for 4x20, it's more of an AU set between 4x17 and 4x19, meaning that in this story, Kate's secret hasn't come out yet.

Disclaimer: If I owned Castle, I would know which one of my theories for the last episodes of season 4 is right, if any. And I would know which spoilers were actually true…

It was the coffee that did it.

The innocent-looking cup of Starbucks coffee held in Kate's strong but delicate hands caused Castle's heart to shatter and land with a thud at his feet.

Starbucks? Really?

Everyone drank Starbucks.

Kate was far too special for such mediocre coffee, a coffee drank by millions of people every day. She deserved the best.

Of everything.

Even coffee.

The guy was a detective. He should have been able to figure that out.

Detective James Striker was the newest homicide detective of the 8th precinct. Striker had moved from London to New York less than six months ago, offered the job with the NYPD before he had even left British soil.

Yeah, the guy was that good. Even Gates had spoken highly of him when she'd informed them he would be assisting on the case. Striker had been called in because the victim had been a well-known member of the British parliament who had been on a two week vacation in New York. Gates had silenced any possible protests by pointing out that Striker's London connections could be a real asset to solving the case.

Castle had liked the guy at first. His mannerisms had reminded the writer of James Bond. Although Castle couldn't imagine James Bond with blonde hair. And the guy looked more like a body builder than a European spy.

But then the guy had asked Kate out on a date no more than two days after joining the investigation. At least Demming had shown Castle the courtesy of asking if there was anything between him and Kate before making his move.

Not this guy.

Kate had said no to the other detective, but her reason wasn't one that made Castle feel any better. She'd given the very legitimate excuse of already having plans with her dad for the evening. Plans that Castle had already known about, which was why he hadn't brought take out to the precinct or invited her to Remmy's or invited the gang to The Old Haunt. Towards the end of that conversation, she had giggled at something Striker had said. Castle hadn't heard that particular sound since she'd received a text from his old protégé, Alex Conrad, over a year ago.

The next day Kate and Striker had arrived at the precinct together, having spent the early morning hours chasing down a lead. A lead that no one had bothered telling Castle about.

Castle told himself he was overreacting. After all, Striker had been at the station when they had caught the break; Castle had been home writing.

The writer then forced himself to shrug off the way Kate was building theory with Striker more than she was with him. It was just because the other detective had been there and knew details Castle had to find out second hand.

But when Castle stepped out of the elevators two days later with the usual two coffee cups in his hands to see Striker hand Kate the Grande sized Starbucks coffee, Castle knew he had to face reality.

It was Demming all over again.

No, it was worse.

Because Striker had even more in common with Kate than Demming had, since Kate's old boyfriend had been a robbery detective. And Demming hadn't looked like a body builder or had an English accent that had more than one female suspect hanging on his every word.

Castle knew what he had to do. He couldn't stand around and watch Kate enter yet another relationship with a man she didn't love.

He needed space, time to think.

He needed to come up with a plan.

But first he needed to talk to Kate.

Dropping the superfluous coffee in the trash can by Kate's desk, Castle made his way over to his favorite detective.

Kate didn't know how much more she could take of this guy. James Striker was a good detective, but that seemed to be the only good thing about him. Any allure his looks and accent may have had was spoiled by his arrogant, self serving personality. He seemed to think that Kate should be bowing and scraping and kissing his feet for the honor he had bestowed upon her by settling his attention on her. 'Out of all the women in New York' he had said. More than once.

Castle at his worst had never acted like that.

It was a strange dichotomy, the way Striker could be respectful of her as a detective one minute and then be so patronizing of her as a woman the next.

Kate could barely suppress a sigh of relief when Captain Gates requested Striker's presence while she spoke with a representative of the Scotland Yard.

Having Castle approach her a moment later only further lightened Kate's mood.

"Detective, do you have a second?" he asked her.

"Sure, Castle, what's up?" Kate said. She couldn't have stopped the smile from forming on her lips if she'd tried. Castle had seemed to grow quiet and withdrawn the last few days. She wouldn't be surprised if he took to avoiding her soon, at least until the other detective was gone. Striker had probably gotten on Castle's nerves as much as he had Kate's. That would explain his unusual lack of crazy theories and childlike antics, which she had missed more than she would ever have the courage to let him know.

"I just stopped in to let you know I won't be coming to the precinct for a while," Castle said.

Kate nodded understandingly. Just like she had thought, her partner had as much of Striker as he could take. She just wished she could hang out at the loft with him rather than having to put up with the obnoxious man.

"For how long?" Kate asked.

"A couple weeks, a month at the most," Castle replied.

A month? Castle actually thought it would take a whole month for them to solve the case?

"Castle, there's no need for you to-" Kate started but was swiftly cut off by Castle.

"Don't worry, I won't make the same mistake I did last time," Castle said. "I'll make sure to keep in touch with you and the boys. I know how mad you all were the last time I went to the Hamptons and didn't call."

The Hamptons? He was going to the Hamptons?

Kate half expected Gina, or worse, Meredith, to come walking into the precinct any minute.

Although that hadn't happened until his going away party, had it?

The thought of having a going-away party for him now made Kate slightly nauseous.

"Is that going to mess up Alexis' internships?" Kate wanted to know, sure that Castle wouldn't be separated from his daughter that long, not so soon before the teenager left for college.

"It would, if she were going," Castle said. "But I'm sure she'll come and visit on the weekends. And Mother will be around."

Kate didn't know what shocked her more. That Castle would leave his daughter in the care of his mother or that he might be alone for the better part of a month.

Except that Alexis was almost 18 and certainly capable of being on her own for a few weeks, especially since she had three detectives and an M.E. who would be watching out for her during her father's absence.

And how did she know for sure Castle would be alone?

He had said he would wait for her, but what if he was tired of waiting?

Kate told herself she was being ridiculous but then she saw Castle glance down at the coffee in her hands. His jaw clenched for the briefest moment before he flashed his signature grin at her.

"So, I'll see your around, Detective," Castle said before heading over to Ryan and Esposito.

Kate looked down at the coffee in her hands and then over at Castle.

Surely he didn't think-?

The last time Castle had left for the Hamptons Esposito had hinted that it was because of her relationship with Demming.

He couldn't possibly think she was in a relationship with Striker, could he? She had never even gone on a date with him, let alone done anything to make anyone think she was interested in the man.

But Castle hadn't brought her coffee.

Castle always brought coffee.

The only other time had failed to bring her coffee was when she was with Demming. Even while she was with Josh Castle never failed to deliver her favorite beverage, day or night.

Kate glanced over at her desk.

No coffee.

Which made her wonder-

She hurried over to her desk, wanting to see if her hunch was right before the writer left the precinct.

And there it was.

Her coffee.

In the trash.

"I want a relationship, not a panda."

The odd words whispered in Castle's ear caused the man to look over at his partner in shock. He had known she was approaching. The scent of cherries always gave her away. But he had figured that she had some new information about the case that she wanted to go over with Ryan and Esposito. Or that she wanted to reassure him that they'd keep an eye on Alexis, which he already knew. If nothing else, he figured that she wanted to get one last parting shot, one last teasing innuendo in, before he left.

The strange statement she had made didn't fit any of those.

He knew what she was referring to. Of course he did. They went back to his own words he had spoken to her a long time ago: Ying needs Yang, not another Ying. Ying-Yang is harmony. Ying-Ying is a name for a panda.

The look she gave him clearly asked, You coming, or what?

As always when she gave him that look, or said those words or a variation thereof, he didn't hesitate to follow her, this time into the break room.

As soon as she closed the door behind him, she pushed him against the wall, poking him with her finger like she had done back in LA. "You threw away my coffee, Castle," she said, her eyes brimming with accusation.

Castle shrugged. "It was superfluous."

"Su…"

"Yes, superfluous," Castle insisted. "Even you don't need two coffees at one time." Or two men to bring them to you.

Kate looked down at the cup in her hand, shook her head, and glared at Castle. "What was I supposed to do, Castle? Say thanks, but coffee is really mine and Castle's thing?"

"You could," Castle shot back.

"Not with that arrogant jerk, I couldn't," Kate said.

Did she just say what he thought she had?

"I thought you liked him," Castle said slowly.

Kate's disdainful laugh made Castle think that he had misread the whole situation. "I have not, nor will I ever, go out with Striker. No matter what he thinks."

Castle, usually with words flooding his mind bursting to get out could only say, 'Oh."

"And as for the coffee," Kate walked over and set it down on the counter before walking back over to Castle, "I couldn't even drink it. All I could think was, 'I can't accept coffee from another guy.' Coffee, for crying out loud! It's not like the guy was trying to get me to go to bed with him. Well, he was, but that's not the point." The very idea made her shudder. "The point is-"

"Coffee is our thing," Castle finished for her.

"Mmhmm," Kate agreed.

"So, what was that about a panda?" Castle asked. "You don't really think Striker is that much like you, enough to be another Ying, do you?"

"No," Kate said, her eyes twinkling with mirth, "but it got your attention, didn't it?"

So what did you guys think of this one?