Kate finds herself watching him at work the next morning, like his actions will somehow clue her in as to whether he's really the one e-mailing her or not. But nothing out of the ordinary happens. He brings her coffee, tosses around a ridiculous theory about their latest case, teases Esposito about the date he had last night that Ryan accidentally told him about. Just a regular day with her shadow.

She catches a spare moment, during a lull in their case, to check her e-mail. Maybe there will be some new tidbit he's offered up. Another clue. But his message gives away nothing. And now he wants to know her name. If this is Castle, and she tells him her real name, will he automatically think it's her? Kate is a common name. But so is Rick and he still went with Alex. If this is even really him at all...

Okay fine. My name is Katie.

So her dad is the only one who still calls her that. It's still her name. It's not technically a lie.

But I did enjoy our chat yesterday. Think you'll be on again tonight? If I don't get stuck at work we should do it again. You're right, it does feel more like an actual conversation than e-mailing does. But you're a writer. You don't mind long e-mail responses, do you? Gives you the opportunity to say more than an IM would.

She reads over the second half of his e-mail again. He's asking about Will. Someone Castle has actually met and knows about. She tries to keep her response as vague as possible.

We were pretty serious. But he took a job in another city and I didn't follow him. And I really don't think he's the reason my friend made me join this site. I still don't understand her reasoning, but I know he wasn't it. Maybe she thinks I work too much. But I think I work just as much as she does. Well anyway, things have been over between us for a while, which is why I think my friend's insistence stems from something else. I do still think about him sometimes though, find myself wondering about what could have been. Do you have any exes like that? Someone you think about and wonder "what if I didn't let her get away?"

Kate scans over the message again, trying to decide if she wants to keep in that last bit. She's not sure why she felt compelled to write that. She has thought about Will, wondered what would have happened if she had followed him to Boston or if he had never taken the job to begin with. But it's not like she still misses him. Even after seeing him again last year, she doesn't feel the need to continually dwell on their break up. Maybe she's just trying to relate to this guy's divorce. Or, well, two divorces if it's Castle.

Her eyes flick over to him again. He's standing in the break room now, talking on the phone to someone. Her coffee mug, which she just now realizes is missing from her desk, sits in his other hand. When did he even take that?

"You know, if he's taking too long to get your coffee, you could just go get it yourself," Esposito teases.

She turns to look at him instead. "No, I just realized my mug was gone. When did he take it?"

"About ten minutes ago," Ryan shrugs. "And then his phone rang and he never came back."

"Some detective you are," Esposito mumbles with a laugh, earning a fist bump from his partner.

Kate rolls her eyes at them and turns back to her e-mail. She decides to keep what she has and hits send before pulling her work e-mail back up. Just as she refocuses herself on the case, Castle sits back down in his chair, placing the fresh coffee near her hand.

"Did you really take that mug while I was sitting here?" she asks.

Castle's eyes go wide like they do when he thinks he's done something wrong. "I, well yeah. There wasn't much left and I figured it was cold so I just -"

"No, Castle, I mean how didn't I notice you take it?"

His face softens and he shrugs. "You were pretty engrossed in whatever it was you were doing. Find a break in the case?"

She glances over her shoulder at the murder board. "No. Still nothing."

"I think I can change that," Ryan says. "The girlfriend just called. Confessed to lying about Nelson's alibi. Which now gives him ample time to have killed Peters before his night shift."

Kate nods. "Bring him in again. Let's see what we can get out of him now."

"And what are we going to do while they do that?" Castle asks.

She points back over at the murder board. "Figure out exactly what to ask him to make him crack."

Castle settles into his office chair and pulls up his e-mail, ignoring the Nikki Heat chapter begging to be written in the background. Katie. Her name is Katie. So another Katherine. Or a Katelyn. Maybe even Katrina?

He's over thinking this.

"Still talking to that girl from the chat room?" Alexis asks, her head popping into his office.

He nods. "Just reading her latest e-mail."

"Yeah? You guys still talking about books?"

"Um," he glances back down at her message. "I don't think so, but I had just started to read it when you came in."

"Oh, sorry. I didn't mean to interrupt," she says, starting to shy away from the door.

"Nonsense," Castle motions for her to come back into the room. "I always have time for you, Pumpkin."

Alexis grins, heading for one of the overstuffed chairs. "So are you prepared to start thanking Gram and I yet?"

"What, are you asking if it was love at first e-mail?"

She smirks at him. "Is that what the kids are calling it these days?"

Castle shoots her a look. "She's very nice and I enjoy talking to her."

"Dad. Very nice? That doesn't sound like an instant love connection."

"I wasn't looking for an instant love connection. I wasn't looking for anything. You and your grandmother are the ones who decided I should be looking on the internet for...whatever this is."

She sighs. "Okay fine, but let me ask you this. Do you enjoy talking to her enough that you're not going to read anymore messages from the other woman?"

He thinks back on the other messages mostly telling him about his "hot single dad" status.

"Yeah I think I'm going to stick with her, with Katie."

"Katie huh?" She's smirking at him again.

"Don't look at me like that. This has nothing to do with Beckett."

Alexis laughs and pushes herself out of the chair. "I'm not the one who brought her into this conversation, Dad. That was all you."

She heads back out of his office and he glances back down at his e-mail with a sigh.

"Nothing to do with her," Castle mutters, continuing to read Katie's message.

Oh wow, she really opened up in this one. Or at least more than she has in any of the other messages. He knows a few people whose relationships have ended because of a move to another city and he knows how much it sucks from experience. That's how he lost Kyra.

Well Katie, it's a pleasure to officially make your acquaintance. And yeah. I do have an ex that I like to think of as the one who got away. And I lost her the same way you lost your guy there. She moved to London of all places on me and I didn't follow her or try to stop her. We met in college, but I still think about her from time to time. I even have a picture of her tucked away somewhere amongst my bookshelves. I wouldn't have the daughter that I have if I had married her, but I still wonder what would have happened if I did. Would we have made it? Should I have gone after her? It's hard to ignore all of the 'what ifs' in life. But I found happiness in my life without her and all I can is hope that she did too.

I know you mentioned you wanted to IM again tonight, but it appears that you're not online right now. Guess we missed each other. Or maybe you're still caught up at work. We could try and plan a time to both be online again. Perhaps that would be easier than leaving it up to fate. Let me know what works for you and your schedule. Because I enjoy long winded just as much as the next writer, but I definitely prefer the conversational feel of IM.

She'd read his e-mail before going to bed, trying to pick out anything resembling Richard Castle from his words. She doesn't know enough about his personal life to know who this ex of his is. But maybe if she can get him talking about exes with her, the one in London will come up. His writing voice is becoming more prominent in his e-mails now. She almost went as far as to pick up one of his books to compare. But she didn't have to because that's the part of him that she knows, the part of him that's been with her since her early 20s.

She still may not have officially confirmed it, but she's pretty sure Castle is the one she's been talking to. Although as she watches him now, gaping at the bride with the deceased bridesmaid, she thinks she may have just found the confirmation she's been looking for in the form of the ex who left for London.

"You two know each other?" Kate asks, hesitantly, knowing she's stating the obvious.

"That would be an understatement," Castle tells her.

She watches them interact for a moment, not even fully aware that she's doing it. He seems so at ease around her. Kate finally gets her thoughts back on the case and moves off to find Lanie to ask her about the body. Her focus lasts only until she walks in on Castle staring after the bride as she walks away with her fiancé.

"Kyra Blaine," he whistles. "Wow."

"I take it she was someone very special," Kate says, watching his face for a reaction.

"She's the one that got away."

She freezes in the doorway as he walks out past her. That's how Alex had described his London girl. It was Castle describing Kyra. She sees that now.

There's a part of her that's still trying to pass this whole thing off as a coincidence. Like there could still be some small possibility that Alex and Castle aren't one in the same. But she doesn't know why she's trying so hard anymore to prove that they're separate people. So she's been e-mailing Castle, so what? It's not like she doesn't already talk to the guy every day. And no one said that this new relationship had to go anywhere beyond e-mails. She doesn't have to start dating Castle just because they met on an online dating website.

But there's something about the way he acts around Kyra that sends a pang straight to her gut. She's never seen him like this and it almost makes her feel something resembling jealousy. But why would she be jealous of him and his ex-girlfriend? His ex-girlfriend who should be getting married right now, no less. So he acts like he might still be in love with Kyra. So what? It doesn't have anything to do with her. It doesn't.

So then why does she feel like she just lost someone she never had to begin with?

"We met in college," Castle starts when the hotel elevator doors close on them. "We were together nearly three years."

Kate glances at him through her peripheral vision. "I didn't ask."

"Yes. You were not asking very loudly."

She smirks at that, recalling telling him nearly the same thing in regards to Will last year. It takes her mind back to their e-mail conversation and for a moment she almost considers just coming out and asking him about it.

"She's different from your ex-wives," Kate muses instead.

He raises an eyebrow at her. "What do you mean?"

"She's real. I didn't think you went for real. Tough breakup?"

She catches the brief pause in his demeanor. The way her words must have taken him back to another place, another time. "It was a long time ago."

Kate knows she should let the conversation end there. Knows that if it weren't for those stupid e-mails she would. But she doesn't.

"I know that it's not really any of my business, but you seem like you're still in love with her."

"Do you ever stop loving 'the one that got away?' I mean you give them that title for a reason."

"You're not going to do anything stupid are you? Like try and talk her out of marrying this guy?"

"I respect the fact that she chose him and not me. It doesn't make it hurt any less, but I respect her choices. All I've ever wanted is for her to be happy."

She bites her lower lip and nods, not knowing what else to say as they step out of the elevator.

"Kyra said you two got stuck in an elevator together earlier today. She seems to like you," Castle tells her.

"She does?"

He nods, holding open the door for her as they exit the hotel lobby.

"She told me that you only dedicate books to people you really care about," Kate starts hesitantly. "Is that true?"

When he looks over at her, she swears he's tossing her that same smile he was using with Kyra earlier. "Absolutely."