A/N: If you haven't watched the sneak peeks for 'The Final Frontier' this won't make a lot of sense. However, should you wish to remain spoiler-free, run away now.

Disclaimer: Don't own then but appreciate being able to borrow them.

Detective Kate Beckett – aka Lieutenant Chloe

As they walk away from Beckett's old college friend Henry, Castle has trouble keeping up; mostly because he's trying not to asphyxiate from holding in his laughter.

"Why the sudden rush Detective?" Castle asks once he catches her elbow, his eyebrows raised, an amused glint in his eye. "You wouldn't be about to destroy evidence would you? Oh, and nice abuse of power by the way."

The flame-cheeked detective, despite her obvious embarrassment still manages to level upon him a 'Beckett-glare' that actually makes his knees quake; and not in a good way. He gulps roughly, but reminds himself that this revelation, is priceless. C'mon Castle, pull yourself together man, he thinks smugly. This accidental glimpse into the geeky history of one Kate Beckett is a dream come true. Oh, the fun I'm gonna have with this information. 'Frakin awesome'.

"What evidence?" Kate asks, trying to keep her tone professional, but Castle can tell she's mortified and he almost feels sorry for her; almost.

"The evidence of your geeky Sci-Fi-fan-girling past," he teases. "You like to dress up. How did I not know this about you, K-Becks?"

Kate steps menacingly towards him and hisses close to his ear, "Call me that again… Kitten, and you'll never see me dress-up in this, or any other outfit." And with that, she tucks the incriminating, less-than-legitimately confiscated photo into her folder and saunters off.

Castle's brain takes a moment to process her words, perhaps because a good deal of his blood has suddenly rushed south. Eventually he comes to his senses and once again he is racing after her.

"Wait. You still have that outfit? Where is it?"

"Yeah Castle, I'm gonna tell you, so the next time you're at my place you can drag it out and play dress-up."

"Hey. Your words, not mine," he says with a lecherous grin. "But just for the record, I'm in full support of some sci-fi-sexy times."

Oh God, I am never gonna live this down. C'mon Kate, use the weapons at your disposal; distract and disarm. So, for the second time in as many minutes, she throws him a Beckett-glare, this one more terrifying than the last and for a moment he actually looks in fear of his personal safety. Mission accomplished.

"You didn't really just say that did you? Sci-fi-sexy-ti..."

He cuts her off then, steps in closer than is strictly necessary, or appropriate given the crowd, but he can't help himself. He has information that Kate Beckett in not only a Sci-Fi fan, which in itself is as sexy as hell but really, he already knew that; but she's also a closet Nebula 9 fan, she has actually dressed up as Lieutenant Chloe and she apparently still has the costume. OMFG this is gold; even better than finding out about her watching Temptation Lane. He is so going to use this knowledge, and not for good. No, definitely for evil.

"Ah Detective, but you seem to be forgetting that I now know your dirty little secret and unless you fulfil my dirty little fantasy of seeing you in that very hot outfit, I may be inclined to divulge what I know."

"And you, Mr I'm-so-smug, seem to be forgetting that not only do I hold the only concrete proof of any of these allegations, but I am also the owner of more than one gun."

"But Kate," he wines as she turns confidently on her heel and strides away.

"C'mon Castle, let's not forget we've got a murder to solve."

When she refuses to let him come to her apartment that night, insisting that they spend the night at the loft, he gives up any hope of some covert snooping to locate the now coveted costume. He is cooking, taking dinner out of the oven actually, when she lets herself in with the key he gave her only a few days earlier and he doesn't look up immediately.

However, when he eventually lifts his gaze he notices her hair immediately. Instead of the soft waves or loose ponytail she favours in her casual moments, she is sporting a tight braid and it's a do he's only seen on her once.

"Is there an ensemble that goes with your new hair-do?" Castle asks hopefully, stepping in close and tugging on the belt of the coat she's wearing.

"Might be," she answers coyly, but then she leans in and kisses him and it's anything but coy.

Her tongue immediately seeks entrance to the warmth of his mouth and he willingly obliges, returning the kiss with equal fervour. They are both breathless and flushed when they draw apart, grinning widely.

"Please tell me Martha is out," Kate pants as Castle begins kissing her neck, while simultaneously unbuckling and unbuttoning her coat. Who says men can't multi-task?

"She's out of the state actually," Castle says roughly against the base of her throat, his tongue laving the hollow there in a move that he knows she loves.

"Thank God, because nobody besides you is ever going to see me in this get-up," she breathes as she sheds her coat.

"Just me and your little 'Trekkie' buddies," he corrects as his heart beats a staccato rhythm in his chest and his mouth goes dry at the sight before him.

The photo really didn't do Kate or the costume justice. It's tight, it's short and now she's wearing long shiny black boots with four inch heels that only serve to draw his gaze along the length of her magnificent legs.

"Dammit Kate, how the hell did any of those college geeks manage to wear those tight pants and not embarrass themselves with you around?" Castle says in a voice now rough with desire, and he presses his hips into hers so she can feel the evidence of exactly what she's doing to him.

Kate chuckles and leans into him; the hardness of his body, the hardness of his… Her train of thought is broken though, when she feels a large hand drifting up the back of one leg, warm fingers curling to stroke the soft skin of her inner thigh. Their lips are fused again and they give simultaneous, breathy moans when Castle's fingers drift higher and make more intimate contact. Holy shit, apparently Nebula 9 Lieutenants don't wear underwear.

As Castle's talented fingers tease and stroke, Kate slides her hands under his T-shirt, briefly drifting her fingertips over his abs, the muscles rippling under her touch before she tugs at the button of his jeans. She manages to divest him of everything but his boxers by the time they stumble and fumble their way into the bedroom.

The only thing she is missing, as they kiss passionately beside the bed, is her boots and uncharacteristically, Castle appears to be in no hurry to undress her. His hands and mouth are all over her and she can feel the wet heat of his mouth on her breast despite the barrier of black and mauve Lycra.

"The zip is in the back," Kate almost whimpers, frustration beginning to fray the edges of her patience as his teeth graze her nipple through the shiny fabric.

"Oh no, Kate. Just in case you decide to destroy the evidence after we're done, I'm going to make sure this little ensemble stays on as long as possible," Castle teases before crashing his mouth back to hers in a kiss that's hot and possessive and makes her knees just the slightest bit wobbly.

When he slips his hand back under the hem of the dress, he's no longer teasing and as his long fingers slide into her, his tongue invades the warm recess of her mouth. Kate clutches at his back as his fingers quickly and expertly take her close to the edge and when his thumb makes firm circles over her she tightens her arms, drops her head against his chest and hangs on for dear life because when she comes, her knees completely fail her.

His hand is still stroking her as the last pleasurable waves die down and when he pulls his hand away she gives a soft moan and nips playfully at his pecs before lifting her head.

"Take this damn dress off," Kate says with a smile. "Call me old fashioned but I prefer skin on skin, to skin on Lycra."

"Is that an order Lieutenant Chloe?"

"If that's what it'll take to get some nudity in this room then yeah, consider it an order."

"Yes Ma'am." Castle grins and wastes no time peeling the costume off her, kissing each new expanse of skin as it is revealed.

They tumble onto the bed once Kate has dragged Castle boxers off and she immediately straddles his hips, one hand fiddling with the end of her braid, the other splayed over his belly. Desire-filled blue eyes meet passion-darked hazel green and Castle lifts his torso, reaches up to grab the end of her braid and drags her face to his. The kiss is surprisingly soft, a gentle pressure and delicate swipe of his tongue over her lower lip.

He grins against her mouth, still gripping her braid as he whispers, "You do realise if you ever wear your hair like this again, I will have to undress you."

"Sounds fair," Kate says as she shifts over him, their bodies making more intimate contact and Castle gasps and bucks his hips. As she lowers herself onto him she warns, "But just remember, if at any stage you call me K-Becks or Lieutenant Chloe in public, I will have to hurt you."

Thanks for reading. This was just a bit of fun so I hope it made you smile. Always appreciative if you let me know your thoughts :-)