A/N: OK, here is where the rating goes up. Shameless smut alert ;)

Kevin fell back against the door after Alexis walked out. He was surprised his legs had managed to walk her to the door without shaking, without giving away some of what he was feeling for her. She was a beautiful young woman; anyone could see that. You'd have to be a blind fool if you didn't. But, she was also a friend and the daughter of another friend, the step-daughter of his boss. And, what he'd told her in their discussion of this "One Day" theory was also still true. He had his career and now he wanted his family; she was still working up to that. He did not want to take any of her young adult freedoms away from her; however willingly she wanted to give them up.

No. One day. That's what she'd said. He could do that, he thought, leaning against the door. One day to hold her, let her turn him on in a way he hadn't been since before he and Jenny had gotten engaged. One day of sex with his beautiful, brilliant, amazing friend. No repercussions. Of course he wanted it. The problem was that there was never a true "no repercussions" clause. So, that's why he'd set the date. Two weeks was enough time to think. Both for him and for her. To figure out if one day of sex was worth the risk to either of their sanity.

Two weeks had NEVER gone by so mind-numbingly slowly. On the night of Alexis's graduation, they'd talked very briefly again. He'd asked her if she still wanted one day, and she'd said yes. So, he told her to come over around 4pm. They could make something for dinner and see where things went. They would have the whole 24 hours. At 4pm on June 5th, she would be on her way back home, back to her normal life, and they would go back to being friends. Nothing more. None of their friends, mutual or otherwise, were ever to know about it. They wouldn't understand. And they weren't going to risk it getting back to Castle, in any way. They were going to be 100% safe and smart about their One Day. Nothing was going to ruin it.

OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

On Saturday, June 4th at exactly 4pm, Alexis Castle knocked on Detective Kevin Ryan's door. Kevin opened his door almost immediately and welcomed her into his apartment. It was far from the first time she'd been in it, but it was the first time she'd been unsure of what to do.

"Relax, Alexis," Kevin closed the door behind her and gestured her into the kitchen. "I'm not just going to jump you. That's not what this is about."

"I know," Alexis laughed at herself, then toed off her shoes and followed him into his familiar kitchen. He had a pile of vegetables out on the countertop, some sliced up chicken breast that it looked like he'd just put into the wok on the stove, and an array of spices next to him that he started tossing in with the chicken. "Stir fry?"

"Yeah, it's easy and one of Javi's recommendations for me to make when trying to impress a lady," Kevin shot a grin and a wink at her. Alexis chuckled again, then set down her bag on a stool and rolled up the sleeves of her top.

"I guess my job is to cut these up?" She guessed, swinging the cutting board and some carrots into place in front of her.

"Mmm, would be nice," he replied, he let his fingers linger on hers as he handed her a knife.

Then he turned up the volume on his phone, which had been set to a music playlist of 60's and 70's music, the Eagles, Beatles, Zeppelin, some Elvis etc. She sang along to the tunes she knew with him and they danced around the kitchen together while chicken and vegetable sizzled away on the stove. As Alexis reached over him to add the last of the kale and swiss chard to the wok, he wrapped an arm around her waist. She let her own arms settle on his shoulders and he tucked his face against her neck. Singing softly along with "Build Me Up Buttercup," of all things. She'd maybe heard the song twice, usually while her dad was going through one of his nostalgic phases, but as she listened to this, with his hands on her waist, lips brushing against her neck every few syllables, she'd never loved a song more.

They turned a few circles, arms around each other, she found her mouth hovering just as closely to his neck as his mouth was to hers. She reached forward with her lips and kissed his Adam's apple, watching it bob a little as he swallowed. His singing faltered and she tried it again, this time kissing the hollow at the base of his throat. His singing stopped altogether and his hand slid lower from her waist to her hips, gently guiding them closer to his own. He lifted his head away from her neck, exposing more of his own for her to kiss and instead contented himself with a soft bite on the tip of her ear. Not something she'd ever considered to be an erogenous zone before, but that gentle nip sent butterflies straight to her stomach. She stretched herself up to reach his lips, but he just chuckled and released his hold on her.

"Easy, Lex," he murmured, voice low and rough. "Food's just about ready."

"Right," she sighed, pulling away from him. "Dinner. Who needs food, anyway?"

Her stomach grumbled and they both laughed. Kevin got a couple forks out while Alexis got a couple bowls and they portioned out the stir fry to eat over at the counter.

As much as it felt like every other meal she'd shared with Kevin over this counter, it was also immeasurably different. She usually had other work she was supposed to be paying attention to, he was usually dead on his feet tired. This meal, they were focused solely on each other. They ate while chatting about her plans for the summer and his most recent case, but somehow, they found ways to touch each other. She wiped sauce off his chin, he let their fingers dance together when he handed her the sriracha.

This routine was easy and she was comfortable. As much as the butterflies were flying in her stomach about what came next, she knew she trusted him and this one day was going to be wonderful. When they finished the meal, Kevin put their bowls in the sink and Alexis walked up to him from behind. She slid her hands around his waist and pressed her lips to the back of his neck.

"Thanks for dinner," She murmured, carefully letting her lips touch his skin, reaching up to kiss under his ear. "I was very impressed."

Kevin chuckled at that as he turned in her arms. She was grinning and he leaned down to place a kiss directly on her lips. Enough of the teasing. Kevin reached around her to the music still playing from his phone and turned his phone off. Not on silent. Off. "One day. 24 hours. I'm not going to waste it on anything other than you."

She blushed as red as her hair, then reached for her own phone and turned it off as well. Their next kisses got deeper, mouths opened, tongues touched tentatively at first, then started dancing together. Alexis sighed into Kevin's mouth and he gave a soft groan in return. He guided her out of the kitchen and they somehow made it to the couch. The wonderful couch that Alexis had always loved. They toppled onto it easily and he lifted his weight onto his elbows so he was raised slightly above her. She could still feel his heat and the suggestion of hardness from beneath the dark jeans he was wearing. It sent warmth straight to her groin as she tried to shift closer to him.

"What would you like?" Kevin phrased the question carefully, gently nipping at her earlobe as though he couldn't actually keep himself away from her.

"What do you mean?" Alexis asked, rather breathless from their makeout session. She'd have thought it obvious. They were going to have sex. Sex is what she wanted.

"I mean," he huffed out a soft laugh and pulled away from her to give them some space to breathe. "What do you want me to do to you?"

"Umm…."

"Ok, let me try again. What have you done sexually that you've enjoyed? What do you want to do again?" He asked, a smirk curling up one side of his mouth. It wasn't that he was enjoying watching her squirm, rather, it was that he was enjoying being the one to open her eyes to this. If their one day led her to being slightly better able to understand her sexuality, then maybe it wouldn't be a waste of a friendship after all. "Is there anything that you want to try?"

"I, uh, normally just do basic stuff? Like, girl on bed, guy in girl? Doggy style a couple times? Not really my favorite, but neither is the groping hands on breasts thing. Guys seem to think I love that, don't know why," Alexis stumbled her way through, not really prepared to talk about sex, just to do it. She should have known he would want to talk.

"We like to squeeze them, we assume you like it too, but you really want something gentler, right?" He asked, his smile had softened while she rambled. He leaned down to focus on her breasts. "I'm going to try something. If at any point you want me to stop, just say it and I will. Ok?"

Alexis just nodded and watched as he lowered his head to her shirt. He shifted his body so that he was kneeling on the couch, knees on either side of her thighs and his hands moved to hold her just under her arms so that his thumbs were barely touching the edges of her bra. He gently kissed from her collarbone down the V of her shirt, his thumbs making slow circles at the sides of her breasts.

As soon as she sighed and let her head sink back into the couch, his hands disappeared. She opened her eyes and lifted her head again to look down at him, but he'd only moved his hands so he could slide them under her shirt. He gave her a questioning glance. Was it ok to take her shirt off? She raised her arms above her head in answer. She was wearing one of her favorite bras, comfort over sex appeal had won out, though it did have a little lace around the edge, it was dark blue with little white polka dot hearts. Kevin just smiled at it and turned his attention back to her breasts. His lips grazed the outer edge of each mound, though he never took the full breast in his hand, he once again let his thumbs wander just on the underside of each. Then, while his mouth stayed on one, his thumb swept over the nipple on the other. The soft fabric of her bra caught at the nipple, and Alexis felt herself hardening, goosebumps prickling up despite the warmth of his breath. He did the same thing to the other side, mouth teasing, a thumb caressing. She let herself sigh into the touch, her body shifting, reaching up to meet him. He reached behind her and undid the bra clasp. She let the straps fall off her shoulders and the bra was gone.

Now Kevin's thumbs were sweeping the underside of each breast while he took a nipple in his mouth. She closed her eyes and arched her back as his tongue swept over the pert nipple, running a circle around it, then over it, then a gentle flick at the tip. As he went to the other side. Alexis let out a soft moan before opening her eyes to watch him this time. His pupils were blown wide, eyes as dark as she'd ever seen them. As he flicked the second nipple, encouraging another arch of her back, he allowed himself a slow grin.

"Have you ever had someone go down on you?" He asked, barely more than a rough whisper, careful not to break her thrall. She couldn't say anything, so she just met his eyes and shook her head.

She assumed he meant something like a blowjob and, while she'd given them before, she didn't exactly have anything down there for him to suck on. Men "going down" on women was never in tv shows or movies or books or anything. It was always women "going down" on men. But after this trick with the breasts, Kevin had free reign to do anything he wanted as far as Alexis was concerned.

Alexis startled ever so slightly as she felt Kevin's kisses sink lower and lower down her torso. He grabbed the belt loops of her jeans and pulled her legs around so she was sitting more upright on the couch rather than laying down on it. He slid to his knees in front of her as he pulled down her pants. She helped him to wriggle her way out of them. Then he resumed his kissing on her inner thigh; his tongue and his teeth contributing just as much as his lips.

The sensation was incredible, the higher his kisses went to her groin, the more she noticed her body start twitching, her legs tensing, hips trying to press closer to him. When his mouth got to her already damp panties, she was a mess. Her hands were clenched into the cushions of the couch and his tongue started tracing patterns against the material. The gentle tugging the fabric made against her sensitive skin felt as if every nerve ending around her clit was on fire. She could feel every breath that he took.

"More," she pleaded softly, practically moaning as she lifted one of her hands to run through his hair, soft curls, no gel. Her plea came out of her mouth as a whimper when he hooked his fingers into her panties to pull them down. His mouth was liquid fire on her, his tongue probing and searching through her wet inner folds. It was amazing how much of him she was just feeling even though her eyes were closed. Kevin's tongue hit her center and she gripped his hair tighter, feeling her whole body tense like a piano wire. As he lapped at her, she whimpered again. His whole mouth closed over her and she felt him start to suck.

She moaned again, louder this time, barely able to hold it in. The lenient, steady, constant pressure right there was incredible. She'd never even dreamed of something like this before. Then his tongue started probing again, slipping inside her. Her fists, which had started to relax, clenched again. A finger joined the tongue and she gasped loudly. Then his tongue was gone altogether, replaced on her clit with a rubbing thumb, forefinger inside her; his mouth, teeth, and tongue reappeared at her inner thigh.

"I….I want…" Alexis groaned, she knew exactly what she wanted, she was so close, right on the fucking edge of something incredible. But she couldn't form words.

"What do you want?" Kevin's rough whispered words came to her from between her thighs. She tried to form words again, but all she made were more moans and whimpers. She was SO close. "Show me."

The words came to Alexis like a dream, of course she could show him. Why hadn't she thought of that before? She reached down, between her legs, to find his hand, she wanted his thumb where it was, but pressed it against herself harder. He continued his rubbing while maintaining this new pressure.

"Unnngggh," she gasped as she searched for just one more little thing. His second finger. She needed just a little bit more pressure inside. She grabbed his middle finger and tried to push it in with his forefinger. It didn't quite work as she was trying, but he understood what she wanted. His thumb relentlessly rubbed at her clit while he turned the rest of his hand so that two fingers could work their way deep inside her. She let her hips grind against him and when his tongue returned to her clit, she practically screamed. A long drawn out gasp. Her hips bucked once, twice, again. She had no control, couldn't think, had probably stopped breathing.

"Hold it," she muttered with the last of her air, pressing her hand hard against his. He stopped moving and simply held his pressure tight against her. She writhed against his fingers, breath coming in gasps and leaving in shudders and whimpers.

"Fuck," she groaned, climaxing hard against his fingers. His mouth, rather than returning to her thighs came up to devour her own mouth. She could taste herself on his tongue, salty and a little bitter, but not altogether bad. She felt her muscles clamp down and convulse against his fingers again and he was groaning right along with her, letting his hard cock thrusting against her hip.

She came down from her high to find him looking just as wrecked as she felt. His lips were dark red, face flushed, hair a mess of short tousled curls, and eyes so full and dark that she could drown in them.

"Fucking beautiful," Kevin gasped, pulling his hand away from her clit to pull off his own shirt and jeans. "You are so fucking perfect."

"Amazing," she murmured, framing his face with her one hand that she'd managed to reach up to him. As she became aware of the hardness he was still pressing against her, she realized that she could take more. She'd never been this wet in her life. They wouldn't need any lube. A condom. Then he could be inside her. She shivered and tried to tell him.

"Condom."

"You sure?" He asked, hesitating slightly before pulling a condom out from the end table drawer.

"Yes," she moaned, she'd never believed that women could have multiple orgasms until right this second. She felt like she would fall apart if he wasn't inside her again very, very soon.

"Hurry the fuck up."

He tried to laugh at her insistence, but he already had himself out and the condom on. After watching her cum, he was wound so fucking tight. He needed to be inside her just as badly.

A soft fumble, a shift in the position of her right leg and neither one of them could speak. Their mouths were hard on each other and he started slow thrusts into her. She clamped her inner muscles down on him the further he went in, she wanted to feel him. She could feel him shaking above her and that made her feel strong. She held him tight against her, rising up to let her mouth clamp down on his ear. He gave a deep groan and lost control of his steady thrusting. He slammed his cock harder into her and she loved it. Harder and faster. Both of them were panting, letting their hips grind together the closer they came.

"Ah, fuck, Alexis," he groaned, shuddering deep inside her. He was so close to the edge before he'd even gotten in her and with her inner muscles clenching all around him, it was too much. He grunted and the stars were dancing on the edge of his vision. He reached down, remembering in his lust exactly what had gotten to her mere minutes ago. The pressure. He held a hand down on her clit. She squirmed again, inner muscles tightening, and fuuuccckk he was coming. He thrust wildly, then held himself as steady as he could because her hips bucking into him was infinitely better than whatever he would do to her. Her entire body tensed beneath him and she groaned out his name, he leaned down, biting gently into her neck, then sucking it to soothe the mark.

Their breath mingled together as they came down from their highs, their lust. It was amazing. Best sex he'd had in a long, long time. She was so responsive and that had aroused him as much as anything. Alexis gasped in air, as if she was drowning. Her whole body seemed to still be shaking. As he slid out of her, she felt the muscles in her thighs twitch. He gave her a sweet, chaste kiss on the lips, before getting up from the couch to dispose of the condom.

"Wow," she murmured as he made his way back to her.

"Yeah," he replied, also still trying to recapture his breath, he climbed over her so her could wrap her up in his arms. He let his lips linger against her skin; he didn't ever want to let her go.

"So, again?" Alexis offered, craning her neck around to meet his eyes. They were a warm, dark blue now, the endless depths of lust had calmed away. He chuckled at her, kissing her forehead.

"Give me a few," he replied, jokingly. She needed some recovery just as much as he did. She nuzzled into his chest, kissing a pec before closing her eyes. She was warm, sated, comfortable, deliriously happy. He never could have imagined anything more perfect than what they had just done. But, he was thinking...

This was a terrible idea. He looked at the marks he'd covered her in, from the tremors that shook her thighs to the bite mark on her neck. There was no way this was One Day. He was hers. Utterly and completely. He should have known.