A/N: A minor flashback is in italics, to help avoid confusion. This is set anywhere between Significant Others (5x10) and Target (5x15).

Disclaimer: I don't own Castle or any of the characters. Andrew Marlowe & Co. are doing a fantastic job...I'm just having some fun.

She had been an idiot. Well, to be honest, she was still being an idiot. And now, she was stuck in the middle of a moronically self-induced fight with her boyfriend, pained words shooting from his mouth like darts at carnival game balloons. All because of two stupid conversations. Three, if she wanted to count the one that had started this.

They had been having such a great night. Castle had taken her out to a romantic dinner at a restaurant with owners who were kind enough to tuck them away in a corner booth, almost entirely unseen by the rest of the patrons as they shared a bottle of wine and some heavenly pasta. Then they laughed through an off-Broadway show, holding hands and stealing glances at each other, as if they hadn't just worked together all day long. But when they were in the town car, headed home, she allowed her wine-loosened mouth to ruin their evening. That mouth could have done dozens of other fun, hungry, sexy things, but instead it just opened up and let the half-drunken declaration come tumbling out.

"I think I know enough about you to fill a pamphlet. Yeah, I do." He looked at her blankly, waiting for her to continue. "No, it's a good thing, Castle. Meredith told me that you knew enough about her to fill a million novels, but she didn't know enough about you to even fill a pamphlet. I was worried. I thought I didn't know anything about nutmeg or your father or anything else, but it's okay because I know a lot of other things, right?"

Castle moved away from her in the back seat and turned to face her. "Meredith? My ex-wife? Was this part of your conversation when you went out with her?"

"No, no, no." She laughed and put a hand on his arm. "It was when she was leaving. I asked her why your marriage didn't work out."

"You asked her what? Why would you do that?"

It was then that Kate's head cleared enough for her to see the flash of anger in his eyes. "Um, I guess I was just curious. I don't know."

"You wanted to know about why my marriage ended, and you didn't think to ask me? What's next? Are you going to call Gina? Look up Kyra? Why not just go down the list?"

"Well, I asked Sophia Turner, too." The damning words were spoken before she registered the thought. Fuck. No more wine. Ever.

Castle sat back against the leather and stared forward, ignoring her completely. Apparently the back seat of a car wasn't his ideal place to have a fight. Kate heeded his silent request and waited until they entered his loft to say any more. When the door slammed, the apologies began.

"I'm sorry, Castle. I don't know what to say." Her head fell forward, her long curls giving her the smallest bit of shelter from his glare. She kicked off her heels, getting a few inches closer to how small she felt.

He threw his jacket over a chair and sharply tugged at his tie in an attempt to remove the noose from his neck. "I just don't get it, Beckett." She flinched at the use of her surname. "You've fought with me over and over again about poking around in your life. Making it clear that it's not my personal jungle gym. But then you go behind my back to ask about my relationships, like you're gathering fucking evidence against me. What's the problem? You can't come up with enough reasons to walk out, so you figured you'd ask your predecessors what they did?"

"God, no." She choked on a sob, desperate to hold back some of the raw emotion clawing at her chest. It wasn't enough to convince him; Castle turned abruptly and stormed toward his office. Kate was left alone in the living room, and her only options were to collect her shoes and go home or follow him and tell the truth. All of it.

"Castle, wait." He had made it to his bedroom door when she caught up with him, and didn't bother turning around when she spoke. Still, he had stopped and that was something. "When I asked Sophia, I was stuck in such a weird place in my own head. I wanted justification for how I felt about you, but I also wanted a reason to run away. I was jealous of what you two had shared, but terrified of ever having it for myself."

He finally twisted in the doorway, just enough for her to see the conflicting love, sadness, and anger on his face. She took a deep breath and kept talking.

"When Meredith was here, I got scared. I mean, once upon a time, the two of you loved each other enough to get married and start a family…but now that's all gone, as if it never existed in the first place. I don't want that to be me. I asked her because I wanted proof that we're different, that whatever ended things with the two of you would be something that could never threaten us. And I admit, when she said that it was because she knew nothing about you, I was worried that I was in the exact same place."

"But you do know me, Kate."

She nodded. "I do. But not as much as I'd like to."

"What are you talking about?" He stepped closer, challenging her. For a moment, it made her rethink her honesty.

"You come across as so open, willing to share everything about yourself. But, Castle, you hold back. You deflect serious questions with jokes, you try to make me answer things that you won't. It's not necessarily a bad thing; I can't possibly stand here and condemn you for being complicated. And I don't blame you for being pissed that I asked your exes about you, but I need you to understand that there were real reasons behind it. None of it was malicious. I was trying to learn more about you, in the process of figuring out us."

The crash of his lips upon hers was sudden, a fierce theft of her breath. While the connection was a relief, she could feel traces of his fury in the way he was grasping at her body, nipping at her lip.

"What do you want to know about me?" He didn't let her answer, his tongue taking any response from her mouth. When he moved to her neck, pulling her hair out of his way, he continued. "You want to know all about my childhood? About how I grew up behind the scenes of dark theaters, my boisterous mother and her larger-than-life friends pushing me to seek solace in the silence of the library? About how I respect and resent her at the same time, grateful for all her sacrifices and angry that I didn't get to grow up like every other kid?"

She gasped as Castle lowered his head and bit her nipple through the silk of her dress, the wetness of the fabric soothing it immediately afterward. Kate's hands found purchase in his hair, pulling him back up to her mouth, ready to meet him kiss for kiss. But he wasn't going to be quiet.

"Or I could tell you about the father I've never met. I've always insisted that I couldn't possibly miss someone I've never known, that it's no big deal. But every now and then, I look around and wonder where he is, how I'm like him, and how my life would be different with him in it. It's an unexpected kick in the gut and it sucks."

Kate tried again, managing to capture his mouth for a moment before he pushed her toward his desk. He spun her around and wrapped his arm around her thin waist, pulling her back against his chest. From behind her, Castle flicked her earlobe with his tongue, and then moved to mark the soft skin of her neck. She arched into him, pressing her ass into his hips; he took the opportunity to place a hand between her shoulder blades and guide her down until she was bent in front of him. His touch started gently, but finished with a contradiction as he roughly lifted her skirt. She spread her legs to give him room, and he reached down to push the damp lace of her panties aside, running a finger through her arousal.

"I wanted to become a writer after I read 'Casino Royale' at age ten. I don't write about murderers because of a childhood trauma at the beach, I do it because I can't comprehend that behavior and I don't like when I don't understand something. You're a mystery I'm never going to solve, but I will devote a lifetime to trying, if you'll let me."

He managed to yank his belt free and unfasten his pants, lowering the zipper and pulling his erection through the hole in his boxers. Castle drove into her with one sudden stroke, only stopping when he was buried deep inside her, the dress gathered around her waist. Kate gripped the far edge of the desk, an attempt to hold herself steady as he rocked into her, his clothes a barrier to the typical slap of his skin against hers. He sped up, and she used her leverage to meet each thrust, his grunts and her moans colliding in midair.

"I'm not entirely sure what happened between Sophia and me, but given that she was a sociopath, I don't think she's the best measure of a healthy relationship. And I walked in to find Meredith straddling her director on our couch, while our baby daughter cried from her crib. Also not something to emulate."

When Castle felt her starting to tighten around him, he stopped moving, holding himself still between her legs. Ignoring her disappointed growl, he slipped out of her and turned her around to face him. Then he lifted her up until she could wrap her legs around his body, and Kate clung to him as he carried her across the office. He kept going until she slammed into a bookshelf, a few novels tumbling to the floor with the force of the contact. He pushed into her again and picked up the pace, sliding in and out of her wetness as she gasped into his shoulder, close to begging for her release.

"And have you figured us out yet? I guess all the books weren't enough to help you. I mean, I wrote about Kyra and Sophia, too, right?" Kate clearly didn't know how to answer, instead choosing to let go of his neck with one hand, attempting to sneak it between their bodies to rub her swollen clit. He caught her wrist and pinned it over her head, against the smooth spines of his work. "So, what if I tell you about everything that hasn't been published?"

He didn't slow, continuing to thrust into her as he spoke, punctuating his speech with small bites along her neck. "There is the letter I wrote to you after our first kiss, our stupid plan to distract a guard in a dark alley. It was the only way I could tell you what it felt like to have you pressed against me, the heat burning through layers of clothing. The only way to describe the sound you made as you breathed into my mouth, resuscitating me when I didn't know I needed to be saved."

"I made a list of places I wanted to show you while we were in L.A., knowing that there wouldn't be a chance to see any of them. I wrote another letter during the sniper case, when I gave you space and prayed that my pen on paper would leave an inscription on your heart."

Castle finally let go of her hand, dropping his under her dress to work small circles against her bundle of nerves. When Kate moaned with pleasure, he took the opportunity to slide his tongue between her lips, dragging the tip along the roof of her mouth. Just as abruptly, he pulled away and spoke softly, whispering into her ear when he could tell she was close.

"I've written thoughts of where we can spend our honeymoon." He sucked on the pulse point that made her clench around him again. "Lists of what we might name our kids, including ones that I guarantee will elicit a famous Beckett eye roll. Enough gift ideas for a lifetime of anniversaries and birthdays."

The promise of a future together is what broke her. Kate threw her head back, displacing a few more books, as the convulsions of her muscles pulled him deeper inside. She seared him with her heat and the guttural noise ripped from her throat persuaded him to let go. With a few final strokes, he spilled into her, his forehead falling forward into the sticky warmth of her neck. Castle's legs wouldn't hold them much longer, even with the support of the shelves behind her, so he carefully let them fall to the floor, still tangled in a mess of sated limbs.

They lay there together for a long time, both of them quiet as they processed everything that had happened. Eventually, Kate found his hand with hers, squeezing it tenderly.

"I'm sorry, Castle."

"I'm sorry, too. I'm just frustrated that we still have problems talking to each other. I thought that we were past that, but I guess it will take some more work, from both of us."

"We'll do it. We'll get there." She looked down at their bodies and laughed. "And in the meantime, do you think we can manage to get undressed?"

He grinned and stood up, reaching his hand down to her. "I might even be able to offer you an actual bed."

Kate smiled back at him, ready to take him up on his proposition. "Thanks. And, Castle? I want to see the list of names."

A/N: As always, I appreciate your thoughts!