Conundrums, among other things (irony, hyperbole, conceit – and unrelated to literature: Rubik's cubes), are inherently intriguing to Richard Castle.

One in particular spends a lot of time occupying his mind, and he thinks that Beckett is perhaps the most mysterious conundrum he's encountered yet.

He studies her, angles and shadows and the sweep of her hair when she bends, and he finds it harder every day not to crumble the stone-wall edges of her mind and let him see - but he knows she doesn't believe that he'll like what he finds as he picks through the rubble.

Even when she's not in front of him he often puzzles on her like a particularly difficult sentence, how her experiences have led her to become so much: a cop, a white knight, (a tease), a collection of contradictions. Why she knows heroin by taste yet she blushes over a dedication in a book. Then his mouth softens. The extraordinary KB. And therein lays the ticking heart of the conundrum he's not sure he'll ever figure out, but knows he'll always appreciate.

He lives several floors above the city but sometimes he still feels surrounded by it, an unceasing ambush of concrete that presses, crowds in. He tried to explain it once, but his mother dismissed him - no one would think to call Richard Castle claustrophobic and don't forget: he is a writer, and lies are his living.

It's a surprise to him that Beckett understands, he expected the rising curve of her eyebrow and that smirk he has come to read as whatever you say, Castle. Instead she just says I know and it happens to the best of us but he can't trace any insincerity in her voice. Her smile sits on the corners of her mouth.

She lets him drag her to a park after work, and they sit with the heat of coffees under a cluster of trees. Castle feels her watching him, and he catches her out. "Something on your mind?"

She averts. "I was just wondering if you were entertaining the idea of stealing another police horse." She lips her coffee cup to hide her grin, tracking two horses wandering through the dusk.

"Are you suggesting something, Detective? Maybe... that you would consider committing such a crime?"

"Oh so you admit it was a crime now?"

"Would you commit it?" He's intrigued now, curiosity mode setting in.

"I don't have to."

Her grin is open when she sees the look blossom on his face.

"I had a really brief stint on the mounted force before I became a detective. I've already ridden a police horse." She looks away, and he hates that he loves her triumph smile.

"So did horses come before motorbikes and bad boys, or after? You know you should have told me, I wouldn't have offered you a pony if I knew you'd already had one."

He'll never forget the night he thought she might be dead. He had thought about it before (naturally), if she woke up one day only to go to sleep with a bullet in her chest, but it was more of a ghost than an entity most of the time; he has enough faith in her to not be as reckless as him.

But that night in the dark, the sear of fire against black sky does more than just haunt him. The possibility that when he went upstairs he might soon be referring to a body when talking to Ryan or Esposito terrified him more than he'd like to admit to anyone, and it stays with him. If he dwells too long it even threatens to eat away at him, sinew, heart, bone.

He remembers, too, that he barely slept the night she stayed over, occupied by phantoms making the lightest creak sound like a fatal gunshot. Without his consent, without the slightest ripple, he has started to care too much.

He also finds that he's started to fit in, and it sits strangely around him, like a suit he's never worn before.

He has always had family, in some capacity or another there has always been that constant, but he doesn't know if he's ever had this kind of relationship before. They're cops, investigators, no-nonsense get-the-job-done types, but they've let him in. Even Beckett, with the biggest hackles of them all, ended up warming to him. And now, with this new kind of family, he has a hard time imagining the seemingly inevitable goodbyes.

However, as much as he enjoys "being a cop", he has never been one for stake-outs (Beckett would cite his attention span as a probable factor in this), and knows he chats too much for her liking.

"You know what Nikki Heat would do right now?"

"No, because we're not the same person, Castle. I don't know why it's so hard for you to wrap your head around lately."

"Blame it on my publisher, she's been calling me every two days to ask how much I haven't written."

"Maybe if you spent less time following me around you'd have more time to write, has that crossed your mind at all?"

"Mine, yours, and hers, it seems."

"So why don't you take some time off?"

"Won't you miss me?"

She rolls her eyes and chooses not to answer.

"By the way, she'd probably have sex to pass the time. Just saying."

They get a case and Castle can see from the first suspect they haul in that its claws have started to dig right into Beckett, who will always draw parallels. He can't blame her, the body count of dead women, women with families (daughters with watery eyes, their hands wringing in their laps) is rising, and every time that bell tolls, the torment drags her closer to drowning in it.

"Sometimes I don't understand how you can stay here so late at night; this place is so creepy when it's empty."

He leans on the doorframe, watches her fingers idle over notes and pictures even as she looks up wide-eyed to see him there.

"Castle? It's past midnight, what's creepy is that you knew I was here."

He smiles, sits down in his chair, notices the upturn of her lips even as she fixes him with a questioning stare.

"I... got... an anonymous tip. Very helpful."

"Ahh." She baits him with a smile, looks back down at the manila folders spread beneath her fingertips.

"You're not going to ask why I came? Not even how I am? I'm hurt, Detective Beckett."

Her eyes flicker towards him for a second, but she doesn't say anything.

She does startle at the thud next to her, the hip flask sitting guiltily on one of the paper piles.

"Nightcap?"

"Castle, we're in the mid-"

"I doubt a few felons are going to care about what you do during your overtime. I'll even go first, just so you know it's not roofies."

She swallows when he does, takes his bait when he sets it back down in front of her.

"Only you would fill a flask with amaretto," she says after drinking some, not bothering to resist rolling her eyes at him.

"So why are you still here?"

She rolls back, pauses for a moment, "I feel like we're missing something, but I just can't put my finger on what."

Standing, she wanders past him. The murder board glares white and she runs her teeth over her bottom lip, arms crossing.

"Could I impart some advice?"

"You're going to anyway."

"After midnight isn't the best time to try and piece together complicated murders." He bumps her shoulder when he sits on the desk next to her.

"I can't lose this one. You know that." She looks at him with troubled eyes, and something in there asks a question.

"I have noticed you're a sore loser." He's happy to see the hard line of her mouth loosen, and then without thinking his hand slides heavily across her jaw, fingers brushing under her ear. His thumb patterns across skin pulled over the bones beneath, and he wonders, as he often does, how such a strong person can be encased in a body that right now seems so fragile to him. It would take nothing to mark it, pierce a hole straight through, and yet she looks as undamaged as the first day he met her. But then, he supposes, the wounds she has scar on the inside.

"Castle. What are you doing?"

He doesn't answer the way he thought he would. He was going for I know you'll be all right, but he murmurs instead: "something I've been meaning to." When he leans in, presses his lips to hers he feels her whole body tense, sharpen. Then, there's the shadow of a grin against his mouth and he grins himself as her hands fist into his shirt. Her mouth opens, and the strength in his knees wanes when her teeth catch his lip, her tongue slicking into his mouth as he stands and pulls her to him. It's definitely not just a little bit of a turn-on, the discovery that Beckett kisses dirty. Her leg angles around one of his, the dent of her heel in his calf sending a jolt up his spine. He sucks down her neck, already feels his heart threading through his fingers to spill out across her ribs.

"Castle. Castle." Her fingers dig in, and he makes a noncommittal noise in his throat, draws his teeth and tongue across the tendon on her shoulder.

"I'm not doing this with you."

He stops, looks at her, her breath heavy and her face glowing. "Am I supposed to be following?"

She pushes him, fingers picking over the buttons on his shirt, tracing the lines of his pockets before they drop, before she backs away. He feels suddenly cold.

"No, look. I shouldn't have... I... this isn't a good idea."

"I'd be more inclined to take you seriously if you hadn't been pressed oh-so-deliciously against me just now."

"I— no, I'm not going to let you— never mind. I need to go."

"Let me what?" He follows her around the desk, and she only stops when she gets to the doorway.

"Do what you always do, Castle. You weasel your way in everywhere even if I don't want you to. This was a mistake, let's leave it at that." She hurries away from him into the darkness of the corridor, and he's left to wonder if this is actually just some kind of mixed up nightmare.

Alexis finds him on the couch, whiskey in hand.

"You okay?" she perches on the arm, fixes him with a look she must have learned from her grandmother.

"Beckett's mad at me," he sulks to her, staring at the bottom of his glass.

"What did you do?"

"Why do you naturally assume I did something to cause it? For once, this is on her."

"Are you going to tell me what happened?"

"No, but I'm going to ask you why I'm so hung up on it."

His daughter smiles, all-knowing as usual. "Dad, they're called feelings. You're allowed to have them."

He looks up at her, managing a smile. "This was much easier when—" the sound of knocking cuts him off. Alexis goes to get it, and he resumes gazing into the amber liquid in front of him until he hears who's at the door.

"Detective Beckett?" Alexis sounds as surprised as he is. He leaves his glass and heads for the door, stopping a few feet away.

"Uh, hi. Do you have a minute?"

"Of course."

With a look to her father, Alexis disappears upstairs and he lets Beckett in, arm outstretched to the kitchen.

"Do you want a beer?"

She nods, and sits at the kitchen bench, nails tapping against the dark granite. "Listen, Castle." He turns to her, momentarily stopped by the uncertainty in her voice, and sees the clench of her teeth inside her cheek. "I'm sorry for earlier. I shouldn't have snapped at you like that."

He shuts the fridge, finds a bottle opener. Popping the cap off one beer, her meets her eye. "Tell me something. Why did you back out?"

She freezes, deer in the headlights. "I... don't think I entirely know myself, to be honest."

"If this is one of those I-don't-want-to-ruin-what-we-have things, you might as well save it because I don't believe in them." The second bottle cap clatters onto the bench top.

She actually laughs a bit at that, shaking her head. "No it's just... I just need some time. You understand, right?"

Armistice is a nod and a beer pushed across to her with a quiet smile.

With Beckett, he's observed that one step back tends to result in two steps forward, and he makes a note to remember that.

They solve the case in the end, the strings tie together and they let bars shut on another killer who won't get out. He knows she feels better, her smile genuine as they ride the elevator downstairs.

As they step out, he looks to her. "So, victory burgers? Victory vodka? Victory... hotel room?" he jiggles his eyebrows, waiting for her comeback as she measures up to him.

"Well, we could do that," he almost feels her voice lower an octave before she carries on, adds a wolfish grin, "but I was thinking more along the lines of wine... me... and a pizza on my couch. Without you." She straightens his lapels, fingers lingering. "Night, Castle." She saunters off, and he can't hold back.

"You know it's just so dirty, you getting off on being a tease."

With her back to him, he doesn't see her smile.

Winter wraps itself around the city, but weather hasn't done much to stop his ideas before.

"The Hamptons. With you. In winter." She likes to make questions sound like statements, arms crossed, that look that always makes him feel like he's doing something wrong. He shoves his hands in his pockets, balls them into fists. He wants to combat the gleeful whining he gets into trouble for, and he almost can't believe she's the one who has made him try to curb his more annoying habits.

A little bit of glee leaches through the cracks. "It's a real house! With real grass, you know. There's actually enough room to throw a Frisbee without hitting an old lady. Unless my mother is outside."

"Who plays Frisbee in winter?"

He leans forward, lets the edge of the desk press into his wrists when he puts his hands on it. "I'll bring you a police horse then. Come on, Beckett. There's a big fireplace, a library, huge tub, might as well be a swimming pool."

He realises his mistake when she darkens, shrinks in. "You know, I haven't really taken a bath since..." she doesn't need to finish, he can fill in the blanks (since the blackness of that bomb went off inside my head; since I found out what it's like to think your own heart might be ripped from you and thrown into a blazing fire that unceasingly gulps and chews).

"The bathroom has a shower too?" He feels like he's lost her, though, she's looking back at her report, frown lines traced into her forehead. He picks up her hand, rests her fingers in one of his palms and covers them with his other.

"Tell me you'll think about it." Warmth seeps around the curves their hands make and she looks down, nods, grips, pulls away. Kate Beckett nutshelled in a gesture.

He does eventually convince her to come to the Hamptons. Or more accurately, he convinces the Captain that she should come to the Hamptons.

He slides the grin off his face right as she comes into the break room, pockets it for later, and feigns innocence.

"Why does Montgomery suddenly want me to use a week of my sick days to go with you to the Hamptons?"

He only shrugs, and quietly basks in her half-hearted glare.

The night before they leave he imagines a montage, in their separate apartments they pack, the thin chords of a guitar playing over her folding shirts into an old-timey brown suitcase stamped with peeling stickers (Beckett is inherently practical, she's probably a thousand times more likely to have a duffel bag or one of those handled ones with the little wheels, but Castle has always thought too romantically).

In the morning he knocks with his elbow, hands taken up by breakfast. Beckett yawns with the sun, pulling itself above rooftops, and she's still in her pajamas.

"I expected better of you, Beckett, we're leaving in five minutes."

The eyebrow arches. "Brusqueness and formal titles at seven in the morning, are we going on a holiday or to a military detail?" She smiles anyway, tows the door back and lets him in; he can't help but feel a small flame kindle at the realisation that he is indeed going on vacation with NYPD Detective Kate Beckett.

They spend their first vacation day in fifty layers, wandering the beach that flows out from their doorstep. He sees her differently out here; this is Kate, someone he saw a hint of once in his kitchen, cooking three different types of breakfast.

When it gets dark they sit by the fire and he can almost see the stones coming out of the wall in her head, and he lets her slip her hand into his as she ends up telling him a lot more than he ever thought he'd hear (most of his topics get shut down, much to his chagrin – not all of them involve leather pants), and she lets a tear or two fall for a mother lost to shadows.

When she goes to bed she drops a kiss at the edge of his mouth and murmurs a thank you, her hand passing over his shoulder on her way past.

After a bottle of wine the second night he decides to teach her to fence, spurred on by the I always kind of secretly thought it was a little dumb she gives him with a smirk at his incredulity.

"You have quite a steep learning curve, Detective, it's almost alarming."

He still beats her in the match, but doesn't count on her grabbing the foil from his hand and twisting him over onto his back, pinning him to the ground. "I'm also quite good at improvisation."

He grins up at her, wonders how long it'll take for her to realise how close their faces are then sees her eyes widen. "Your move, Beckett."

Adrenaline, wine, recklessness, he thanks anything he can think of when she closes the gap and kisses him. He's fairly certain he could make out with her forever, if it came to that.

He finds her in the library more often than not over the next few days, mulling over titles and wedging herself into the corners of the ornately patterned armchair he likes so much himself. She always looks up when he wanders past, her smile for once utterly unperturbed.

"I keep forgetting we have to go back." She rests a book on her knees, watches him lean against the desk next to her.

"We don't have to, you know. The Captain says you've stacked up enough sick days and unused leave to take a vacation for over three months. Seriously, do you know what holidays are?"

She looks at him, and he can't quite figure out her expression. "If I stayed here it would feel a lot like running away." Her eyes cloud over.

"From what?"

"At home I have to be a cop, I have to be rational, be an adult," her eyes flick to him, "keep my feelings in check so I don't jeopardise what feels like my whole life. Here, there's no weight on my shoulders but I also feel like I'm just sidestepping responsibility."

He can't argue with that.

Esposito and Ryan crowd him at the coffee machine the morning he and Beckett get back.

"If this is about a bet, we didn't sleep together. If it's because you missed me then aww, that's so sweet, I'm glad to see you guys too!"

He wonders how long it'll take them to figure it out.