Small reminder that this chapter strays into mild M territory.

Chapter 5: A mystery cat

Beckett forces herself to do her chores the next day, which is a duty that she dislikes at any time, but especially today. She is having a very hard time controlling her urge to go to the loft, and she's having an even harder time not telling Castle the truth. It's Castle, after all. He believes in everything. If she gave him a rainbow unicorn he'd accept it as real and say Cool!, where everyone else would be looking for the surgical stitches and claiming it was a mutilated pony with a cheap dye job.

She has to take this slowly. She has to be absolutely, positively, definitely, incontrovertibly sure that it's real; he's the one; she's the one. Because her whole life will depend on Castle keeping his mouth firmly, totally, shut; on him never revealing anything to a single soul.

Because if he ever did, she'd have to leave. Change her whole identity. She'd never be able to be a cop again, because one run through the databases and she'd be known. A real shapeshifter? She'd be a media show; a story for every quiet news day. And worse, she'd be studied. Examined and investigated; poked and prodded and DNA tested and made to change till they discovered how. Magic doesn't cut it as an answer when the scientists get interested. Scalpels, however, would.

He hasn't suspected anything yet, thank heavens. It doesn't seem to have crossed his mind. So it's okay. She can go over this afternoon – yes, this afternoon, not now – and take a DVD, and snuggle up, and kiss him. That'll show him she's into this. She'll take Forbidden Planet, since he'd said he loves it, and if he's seen it lots, it won't matter if he's not paying attention. She hopes he won't be paying attention to the film.

She grumbles and mutters and does her chores and resolutely does not call, text or visit Castle until after lunchtime, of which she manages to partake, with astonishing self-discipline, at the normal time, rather than eleven a.m. Some of her frustration is no doubt because last night's petting didn't include quite enough ear-fondling to be wholly satisfying, and as a cat she can't tell him what really, really makes her happy. Now that she knows what Castle's hands can do for her, her own fingers and toys are not nearly as good.

She congratulates herself on her self-discipline all the way to Castle's loft. Then she congratulates herself some more for not simply jumping him as soon as she enters, though that has more to do with her still-sore bruising and creaking than anything else. She is presented with coffee, curls up in a corner of the couch, and listens to Castle complaining about the lack of cat to meet her. She replies with a considerable number of putting-him-off-the scent comments, which seem to work. Though there is a nasty hitch when he enquires about her health, and then stops dead after saying Same as Onyx. However, he starts the movie and his lips are moving along with the lines, so he can't have jumped to any conclusions. Phew.

Far more usefully and pleasurably, she hasn't even had to move before he's draped an arm around her. She responds by cuddling in, then drops her head on his shoulder and puts a hand on his knee. That should give him a clue or three. Happily, he takes them. His arm slides down and around so that his hand is on her hip, and she wiggles to be entirely tucked in and cosily warm. Ohhhh, this is just perfect. Now, will she need to make another move –

No. Because Castle has tipped up her chin – oh, ooops, she's purred even before he's kissed her. That's not a proper kiss, though – and she opens under him, licks along his lips and demands entry, to which he accedes instantly. She stoops, swoops and conquers: taking his mouth as if she'd always had the right; and oh, he's so good at this, letting her raid and then ravaging himself; she's heating up faster than oil on a griddle but she can't do anything that might make her wince, because he'll stop, and she'll have to stop, and she doesn't want to stop. Her hand has sneaked on to his shoulder, and she'd love to be on his lap and then all sorts of clothes-opening would be possible, but he's being cautious with his hands (humph!) and she's not going to risk this being messed up again like it was yesterday.

She keeps kissing him, showing with every sweep of tongue and nip on his lips that she wants this, and him, until he pulls off and stares at her with midnight eyes and sheer desire. His words fall out of his mouth with no input from his brain at all, and she smiles inscrutably and teases him with more words. He responds in kind, claiming that she's mean. Well, yes, of course, but not malicious. But – if she was a cat she'd be playing with her prey? That's far too near the knuckle. She feels the urge to change to her panther, and show him exactly how a big cat plays with its (sexual) prey, and only just resists.

Instead, she makes sure he knows he's invited over tomorrow, and sinks into his farewell kiss for far longer than she'd intended. She could spend a lifetime in his arms, in his kiss, tucked against his broad bulk; safe, cosseted, cared-for and loved. She manages – just – to bid him goodbye, and to go home.

She counts every second of every minute until she can leave again: telling herself it's ridiculously teenage, that a mature woman – or feline – does not let herself be totally enraptured by anyone. She entirely fails to convince herself, and, as Onyx, is back with Castle by dinner time, feeling delightfully happy, content and ready to be petted as extensively as normal.

Besides which, he's sure to tell her how he felt about the progress of their relationship, and then she'll be able to plan the next step of her careful seduction.

It all starts to go shatteringly wrong after dinner. Castle thought she might be Beckett in disguise? What the actual fuck. He can't think that. Even Castle isn't that insane. And by the way, Castle, it is not flattering that her lovely Onyx-form is not as fitting as a panther, tiger or leopard – though she's the first of those too. She regards him with annoyed dislike, and he admits that it's nonsense, and he's being silly. Good. Hold that thought, Castle, for a long time. He invites her up, and she curls against him to be stroked. That's better. Lots of lovely firm stroking. She could stand a considerable time of firm stroking, and not just as a cat. She thinks about firm strokes and purrs happily. He expresses concern about Beckett-human, and she miaows and curls in even more, so that he plays with her ears in that wholly erotic way that simply does it for her, and it does.

And it would have done again, if he hadn't gone back exactly where he shouldn't. Looking up shapeshifter detection devices and methods? Ugh, ugh, ugh. She glares at him viciously. He won't be feeding her any of those. No way. And while he's researching, he's not focused on her, which is also not acceptable.

However, he hasn't found anything useful. Good. Castle might be pouting, but she's relieved. She snuggles over his chest and accepts his petting as only her due, sinking into a contented haze of sensuality which lasts all evening. He seems to have given up searching for something he won't find.

In the deep of the night she slips away, ever more regretful. The cab drops her at her door, and she changes and sneaks in, invisible in the dark. She always sneaks up late at nights as a cat. It prevents anyone noticing her, and it's only one floor. The stairwell door is easy to push open, and she prowls out –

Oh, shit! Her nose picks up the scent of Castle's aftershave almost as soon as she's out of the stairwell. How the hell did he get here? Why did he come here? He couldn't have spotted her leaving – could he? He's slept like the dead every other night, why should he wake tonight? She tries to retreat before she's spotted, but Castle moves far faster than she'd ever thought he might be able to and catches her.

"What are you doing here?" he asks. She really doesn't like that gently enquiring tone. It's far too close to her own, as used in Interrogation. She doesn't like the note of I want answers, either. This sounds far too much like Castle having reached some entirely correct conclusions. Why does he have to have a mind as broad as Montana? Nobody else would even have thought that she might be a shapeshifter, still less investigated it. "More to the point, how did you get out? Last I knew, cats couldn't manage door handles. Not mine, anyway."

He picks her up. This is not an improvement. "I thought it was all a coincidence, but it wasn't, was it – Beckett." Oh, hell. He really has worked it all out. Damn, damn. She spits and hisses angrily. "You wouldn't know how to come here unless you lived here, and if Beckett had had a cat – you – she'd have taken you back as soon as I showed her the photos." Beckett loses her feline cool, and takes a hopeless, infuriated swipe at him. All that gets her is Castle taking a firm hold of her front paws. "How'd you do it?"

She makes frantic efforts to escape him, twisting and wrenching, hurting still-unhealed bruising, manages to elude his grip and leap away, but when she hits the floor it's agonising and she can't quite get through it to run before he's trapped her again, folding her in to stop her kicking and scratching, calm strength proof against her desperate efforts to get away, to protect her secret, to hide. Eventually, tired and in pain, she stops, and simply fixes him with an evil glare, ears flat, tail lashing, more furious with herself than him.

If only she'd been more careful. If only she'd taken a sniff of the air before she opened the stairwell door. Now it's all ruined.

"Stop running away, whoever you are," he says, but it's all too horribly clear that he's dead certain she's Beckett. Especially once he notices the cat-flap. Why'd he have to be so damn smart? She droops, utterly unhappy.

"C'mon. I've worked it out now. You might as well admit it. Besides, this is so cool. I can't believe you really exist. It's amazing. Fabulous. Fantastic."

Freaking typical. Only Castle could be that enthusiastic and instantly believing. His fingers are already starting to pet and stroke.

"If I let go, will you open the door?" he asks, all his tones hopefully persuasive. "I think we've got a lot to talk about." He strokes her gently, which is absolutely not fair because she's already melting under his touch, sensations wriggling along her spine, and it is totally unreasonable that she just wants him to keep petting ohhhh just like that. She shouldn't be seduced into concessions. "A lot to talk about," he pleads.

She looks at him, no longer fighting, trying to understand if she can trust him. It's too late if she can't, she realises. She has one chance – and she can either blow it now, or believe in him.

She climbs on to his shoulder, butting her head into his neck, and hopes like hell she's got this right. His clever, caring hands stroke her, and she gives in. She purrs. "Okay then, deal," he agrees, and lets go to allow her to slither through the door.

She changes to Beckett, and opens up.

Castle simply gathers her in, as close as he can, leans his forehead on hers: the same sincere caring that he'd only shown to Onyx: holds her yet, truth in every second; until at last he runs slow, gentle strokes up and down her spine, just as he would do for Onyx, somehow knowing that in either form she's pettable.

"I've got you. Whoever you are, I've got you and I am keeping you," he says, confident that she'll not deny him. He tips her chin up, just as he had earlier, and kisses her with the same passion and power: taking and giving and demanding and receiving. She slides hands round his neck and pulls him down and back to her lips: opening for him and arching against his width, sensing the swelling firmness pressing into her with delight; squirming closer and never stopping kissing him.

When they stop, she'll have to talk. She kisses him further, delaying as long as possible, but eventually he lifts away, which is unwelcome, sits them down with her in his rather over-excited lap, which is better, and asks her not why, but how?

Well, she's not telling him the whole history. Besides which, though she does now know how, a girl – or cat – has to keep some secrets. The man is practically bouncing with delight. Honestly, what a child. Anyone would think all his Christmases had come at once. Just because he's found out that shapeshifters – one shapeshifter, she's never found another one, which is why she's currently in this position– exist, he's behaving like he's had a new toy. He wants a demonstration, and whines pathetically until she gives in, and then he's even bouncier. It's like having a human trampoline, there's so much bounce.

Of course, this is Castle. Of course he's interested in the clothes. Or lack of clothes, more like. There is some very sensual mischief dancing in his eyes, and she's quite sure he knows perfectly well that his fingers are still stroking, cat or woman.

And then he works out something she'd really rather he hadn't.

"You spied on me," he growls. Well, yes, but spied is such a nasty way to put it. He didn't have to take the cat home. "You cheated." Not at all. All's fair in love and war, Castle. Doesn't he know that? He's promising her wicked things, though, as she flirts with him, and she's reacting to that, and the fidgeting fingers. Unfortunately he's not quite distracted enough. Yet. In true Castle fashion, he just keeps pushing – and then he works out exactly why she'd originally padded down the alleyway and she's sure her blush could start forest fires upstate in winter.

"I like petting you," he says in a velvet tone that strokes her nerves all the way down. "Cat or not." And he begins. The first stroke is slow, smooth and sensuous, from head all the way down to where her tail would be. She curves into it, and he glides around her hip to land on her thigh: close but not quite close enough. She's already aroused before his warm palm meets the soft skin of her waist: the first time he's touched there in human form. His light touch scorches.

He leans in slowly, intent in every lineament, and she falls into his mouth without a single hesitation. The fingers that were so incredibly good at petting a cat turn out to be as arousing when she's human: sliding up under her t-shirt to skate over her back and press her in, easing a fraction as she opens his shirt and then, her tee discarded over her head, she turns against his skin and surrenders to every erotic, arousing sensation. His hands skim over her, learning as they go; his mouth doesn't move from hers as he lays her a little back and palms her breasts: as good as fondling her feline ears, bringing a moan from her lips and a purr following it as he plays and pets. She's soaked and he's still playing with her, but her hands are wreaking some erotic havoc of their own.

He stops kissing her, which he shouldn't do: she scratches very lightly and emits a small, disappointed noise, but when his mouth slips behind her ear she opens her throat to him as any feline might do and pulls his head down. She's already so close, and then he nibbles downward and starts to play again and it's all flowing south: he teases her and tantalises, plays with the soft skin – she's still too sore to wear a bra and he's loving that – a tiny, gentle nip, a suck, and she's gone on a long, soft sigh.

"Take me to bed," she purrs seductively. "After all, I've spent plenty of time in yours."

"Come here, then. You don't need to be a cat for me to carry you to bed." He sweeps her up, stronger than she'd expected, and kicks her bedroom door shut behind them, stands her up and presses her in, hard against her; slides off her sweatpants as she's pushing away his button-down; resisting just a fraction as her wicked hands move to the front of his pants and explore.

"Naughty, naughty," he smiles. "So impatient."

"Turnabout is fair play," she husks, and flicks his pants open, long, delicate fingers slipping inside to explore and tease; circle and slide. Castle groans, and takes her mouth with an aggressive kiss that lights them both up. His pants hit the floor. Beckett hits the bed, Castle over her, pulling him down to her so she can arch and rub against him, he's ripping her panties away and discarding his boxers and there's no more play, no teasing, no need because she's soaked and he's rock-hard and then he's finally, finally within her where he ought to be and there's no more thinking, just the man and the moment.

Castle slips off her, and pulls her across him so that she's tucked over his chest and he can stroke her hair and down her back, which he does, just as he would if she were Onyx. She nestles in.

"That's better," he rumbles. "I like you just as much this way." His petting strokes up and down her spine. She flexes against it, and murmurs contentedly, and then curves her hand around his stubbled jaw. His smooth stroking reaches a little further down each time, gliding over the taut swell of her ass. She shifts position a fraction, curling one leg around him in opened invitation. His clever fingers take slow advantage, slicking through her, easy, unhurried touches. She turns her head against his pecs and lets her tongue stray, twine around his nipple. There's no rush. Slow can be very, very satisfying.

He begins to rise and fill against her again, as she is becoming hot and wet under the delicate, drugging movement of broad, long digits and the flex of his thighs widening her for him. She moves sensuously against him, as flexibly as the cat she is, and he makes a low noise deep in his throat before she kisses him into silence and slides against him to take him in once more. He fits perfectly: hard and long, deep within her; and for a moment they're both still, joined as close as they can be and learning each other's intimate spaces.

"You feel so good," he murmurs, and she wriggles just a tiny amount and hums, because he feels just as good but she doesn't want him to stop kissing her because that makes it feel even better. She moves slowly, and he slides her back equally slowly, large hands spanning slim waist; until slow slides merge imperceptibly into harder thrust and then there's only her and him and them and bliss.

"Will you still be Beckett in the morning?" he asks her, stroking gently over her side.

"Whoever you like," she says, and tucks her head into his neck and her arm across him, so that her head is just where Onyx would have been.

"I like you both," Castle says, utterly satisfied. "It's just so cool that you're my cat."

Fin.

Thank you to everyone who's come along with the Cats' adventure, and especially those who have reviewed, guest and named.

I'm not sure when the next instalment of the Cats will be, since I'm still writing it and it will be more than a two-shot. Also in progress is a serious story. I am not abandoning this fandom.