Disclaimer: The only part of Castle that I own is the TV on which I used to watch the show.

A/N This chapter has an M-rated section that begins with "Couldn't be more sure." If you want to skip that part, scroll ahead to: They're spent, but after a few minutes he croaks, "How the hell did you do that?"

It took everything she had to knock on his door and ask if he's awake, but there has been no response. She shifts from one bare foot to the other, and regrets not having put on any slippers, or at least socks. Cold feet, she thinks. I'm getting cold feet, literally and figuratively. Platitudes chase each other inside her head. "Throw caution to the winds." "In for a penny, in for a pound." "Nothing ventured, nothing gained." "A journey of a thousand miles begins with a single step."

Gah. She knocks again, but this time doesn't speak. When she's counted to a hundred and he still hasn't opened the door or said something from the other side of it, she peaks underneath. She can see light, so he must be up. He couldn't have fallen asleep with a light on, could he? He hadn't seemed at all tired when she'd gone upstairs, and that wasn't long ago. After counting to a hundred again she agonizes for a while and decides to make a huge leap: she turns the knob and crosses the threshold, taking the single step on what she suspects could be the beginning of a lifelong journey.

Because she's concentrating on being as quiet as possible, she doesn't see him until she has carefully closed the door behind her. When she turns around she finds him standing in the doorway between the bedroom and bath, wearing nothing but a towel around his waist. His hair is wet and so is he. She is briefly transfixed by three shimmering drops of water that are making their way down from his clavicle, bisecting his chest, and trickling towards his belly button, which is visible just above the edge of his towel. When they disappear from view, she looks up.

"Beckett?" It's two baritonal syllables of utter astonishment.

The only thing that's more astonished is the expression in his eyes, which look bluer than usual because of the blue towel–which she now notices is not very big, or maybe it is but there's just so much of him. He's so big. How had she not noticed this before? He could probably register his calf muscles as lethal weapons. And his biceps, holy mother. He could probably balance her on one of them. There's a thought that should perhaps go unvoiced for the moment. She's not sure that she has a voice at the moment anyway. She tries it out. "Sorry." Not strong enough. "I'm sorry. I knocked a couple of times but you didn't answer but the light seemed to be on and I thought it would be okay if I came in and, you know, checked. On you. Checked on you."

"I was in the shower," he says needlessly, gesturing over his shoulder.

"Right. I see. I mean, I figured since you're"–her hand flutters to her head–"wet."

"It's noisy. The shower. Has a lot of jets. I had it on full force."

"Right."

"So I didn't hear you."

"Right."

They're rooted in place, staring at each other.

"It didn't work."

She's confused. The shower didn't work? Did he take a bath? Then why did he say he had the shower on full force? "It didn't?"

"No."

"Well, you look very, er, clean. So it must have worked." Maybe she should look at his feet, which are far less distracting than other parts of him. Unless she can't prevent her eyes from wandering upwards a few inches to those calves, and apparently she can't. She's working very hard not to speculate about his thighs.

"I took a cold shower."

That gets her attention, and she redirects her gaze to his face. "You did?"

"It worked fine until you appeared in your nightie. Nightshirt. Jersey. Top. With no–. With your bare legs, which by the way, have you ever measured? You're five nine, right? But that can't be right because your legs are are least five feet long."

"They are?"

"Maybe longer."

"Oh. Listen, I was thinking about what I said before. About being tired. Worn out is what I think I said." This is tough. Can't he get the drift and help her out? Help them both out? She hasn't felt this awkward since eighth grade when Lucas McGuire caught her skinny dipping in the pond behind the cabin.

"Right."

Dear God, that's what she'd said to him about the shower. This is hopeless. They're hopeless. Suck it up, Kate, she tells herself. "When I got into bed I discovered that I wasn't tired, after all." She pauses. He's still in the same spot, like some glistening god, but a god who has mysteriously lost the art of conversation. "And then I was thinking that Martha and Alexas are away." Another pause, but the god remains statue-like. "So I decided to come down here and give you the goodnight kiss you asked me for."

He moves a tiny bit, not quite a half step, but something. "You said you already did."

"I did. But you know what? I want more. A whole lot more." Here goes. "Do you?"

"Yes, but–but are you sure?"

"Couldn't be more sure. Drop the towel." When he reaches her–that god can move!–he undoes his towel with one hand, and with the other peels her jersey over her head and lets it fall onto the floor. "I see what you mean about the cold shower not working," she says, any filter that might have been in place now gone. She'd thought he was big before? Oh, this is going to be something. Before another coherent or incoherent thought can make its way through her mind, he picks her up and she wraps her legs around him, her feet locked near the base of his spine.

"Oh, you're definitely sure, Kate," he whispers into her ear as he walks them both to his bed. "I'm not the only one who's wet."

"That's pretty dirty talk for a clean guy," she says, and they're both laughing when he drops her gently onto her back on the mattress. She scrambles up so that her feet aren't dangling off the end of the bed, and by the time she's there he's already nudging her legs apart. He's tickling her behind her knee–how did he know that it's one of her Top Spots?–and at the same time licking his way up her thigh. Even his tongue is big, it feels big against her skin, flat and soft and warm but also sizzling. It sends her into some kind of frenzy that escalates into something previously unknown when his tongue stops licking and begins to probe.

"Yum," he hums against her, the vibration making her back arch. "You're not just gorgeous, you're delicious."

"Up here," she manages to say, releasing her hold on the sheet to brush her hand across her breast.

Very briefly, he lifts his head. "You want me up there?"

"And down. Both, both."

Which is why his tongue is now doing something indescribable to her left nipple and two of his fingers are doing the probing. They've reached her G-spot, and they know–Castle knows–exactly what to do. Some brilliant bit of dexterity, with thought behind it, that she has never experienced. When he executes it, this combination of pressure and flickering movement, she comes faster and more wildly than she ever has.

"Wow," he says, after narrowly escaping a black eye when her knee glanced off his cheekbone. "That was–I don't know what, exactly. Stupendous. My writer's wits have deserted me."

"How the hell did you do that?" she asks, still short of breath.

"Inspired. You inspired me. I didn't know you'd be my muse in bed, too."

"You never did that before?"

"Not that way. Never."

"Hang on."

"Gladly."

She feels the sweat evaporate from between her breasts, and her heartbeat return to normal. She's sure that he doesn't expect her quick move, as she flips him onto his back and then straddles him. "You have magical fingers, but I want more. I want this." She rises up a few inches and then, leaning forward, strokes him lightly before sinking down on him until he's fully buried. "Oh, my God, you're so big."

"Am I–"

"No, no, no. It's fantastic." She rocks forward, and her hair brushes across his shoulder. "I could do this with you forever."

It's not forever, but it's as long as either one of them can remember. They are madly energetic and vocal and seemingly perfectly matched. With every twitch and every contraction, every push and every pull, they urge each other on. He drives into her as hard as he dares, but she latches on to him and says, "harder." They both want release, and they both want to hold it off as long as possible. Finally, she explodes, and three thrusts later, he follows.

They're spent, but after a few minutes he croaks, "How the hell did you do that?"

"Do what?"

"That thing with, you know."

"Oh, that? Spur of the moment. I guess you're my muse, too."

She wakes up much later, and when she rolls over he wakes, too. "Hi," he says.

"Hi." She looks at him and smiles. "I don't usually do that."

"What, have sex on a first date?"

"Was this a date?"

"Good question."

"I don't usually make noise like that. So much. That loud. Good thing we're the only ones here, huh?"

"I loved the noise. It's music to me. You were Mozart. You were Alicia Keys."

She giggles. "More like a heavy metal band."

He cups her shoulder with his hand and draws her into his side. "Don't worry about it."

"I have to worry about it. This isn't just for tonight, is it? I mean, I'm not a one-night–"

"Shhhhh. Shhhhhh. Don't say it. Don't think it. You already know you're it for me. You must know that, especially after the last couple of hours. Besides, you read it in that file I so stupidly and brilliantly left out on my desk before I went to Philadelphia." He inhales against her hair. "I don't want you to worry about making noise in bed. I don't want you to be afraid to sneak down here again tomorrow night and the next night and the next night. But I have an idea."

"It better not involve going to my apartment. I don't have one."

"No, my idea is that in the morning I'm calling an acoustical engineer and getting this room sound proofed." After he's made that cheerful announcement, they talk softly about important things and frivolous ones; things they used to do and things they'd like to try; things that matter to one or to the other but now, on their new shared yet untested ground, matter to them both. At some point he drifts off to sleep in mid-sentence.

She, on the other hand, is wide awake, brain buzzing. She's curled against him, watching his chest rise and fall as he breathes, watching his eyes to see if they move beneath the lids. When they do, she wonders what he's dreaming. Is it about her? Them? The work them, or the now personal them, or some combination?

Castle is the optimist, the one who believes that everything, or almost everything, will work out. She lives in a gray world where nothing is black or white or certain; everything is shadowy and shaky and unknowable. He's had two bad marriages; she hasn't even risked living with someone. And yet after only a week under his roof and only a few hours in his bed, she's ready to bathe herself in his confident hopefulness. Ready to think that they can be together, will be together, that they will thrive. She's still in his arms, a position she has never before been in for more than a few minutes. In the past, with other men, she has always felt trapped, wanted to withdraw, to get away, but this seems natural. Inevitable. Wonderful.

She tilts her head slightly and continues to look at him, at the slight bump in his nose, at the strong chin. The darkness in the room is not complete, and she takes inventory. All the pillows are on the floor, though she has no memory of how they got there. She smiles with the realization that she could make an informed guess, but it doesn't matter. The duvet is in a tangle and has slid most of the way off the bed. Although it's very cold out, it's officially spring. Maybe the season of rebirth has affected her mood, too. A few lines of an Edna St. Vincent Millay poem she read years ago, a favorite of her mother's, flood her memory.

Beautiful Dove, come back to us in April…
Come back to us, be with us in the spring!
If we can learn to grow the grain you feed on,
You might be happy here; might even sing.

That dove, she could be that dove. She doesn't have to fly away. She might be happy here, might even sing. If it wouldn't wake Castle, she'd sing right now. What time is it, anyway? Her phone is upstairs and his is on the nightstand on the other side of the bed. It must be after five, maybe even close to six. Oh, shit, it's Monday. She has to go to work. She has to take a shower and hope that any marks that Castle left on her–she hasn't checked, but she knows that there are some–can be hidden under her clothes. She wriggles out from his unconscious embrace, creeps out of the room and up the stairs.

The shower is divine. She stays in longer than usual. The water temperature is perfect. The soap is perfect. The shampoo is perfect. The conditioner is perfect. She finds herself singing "Oh, What a Beautiful Mornin'," another favorite of her mother's and something she hasn't even thought of in more than 20 years. It's as if some switch has been activated, and the music pours out of her of its own accord.

Swaddled in a soft bathrobe, she dries her hair, still singing verse after verse of "Oh, What a Beautiful Mornin'." After quickly applying eyeliner and mascara, she opens the door to her bedroom. On top of her bureau is a mug of coffee. It's the WORLD'S GREATEST DAD mug that she had bought, but there's a pink Post-it note pressed over the last word, with another written in its place. The message now reads WORLD'S GREATEST DETECTIVE. When she picks up the mug to take a sip, she finds two small things behind it. The first is a Hershey Kiss with an almond. The second is a scrap that Castle must have fished from the wastepaper basket. "Nice song," he'd scribbled on it. She looks at it again, more closely. He'd also added a tiny heart.

TBC

A/N Thank you again, kind reviewers and readers. I'm back home now with fully functioning internet. To my friends in the north, happy Canada Day tomorrow. To guest reviewer Chacha: yes, there really is such a thing as chocolate peanut butter ice cream. Häagen-Dazs makes it.