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A Pretty Good Bad Idea

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“This is stupid.”

“Your face is stupid,” Derek responds automatically. 

Casey glares at him in response for barely half a second, before raising an eyebrow, “Really, Der?”

“A little,” he starts, as he closes the hood of her car, and walks towards where she’s waiting, “Depends on the face you’re pulling.”

She rolls her eyes as he leans against the side of the car next to her, wrapping her arms around herself, “How bad is it?”

“Fucked if I know, apparently I know even less about cars than I thought,” Derek admits, “There’s an engine in there? I can tell that much. And I think there’s enough water for the wipers.”

Casey smacks him on the side of the arm, even as she’s smiling a little, and he ducks his head to the side as if he’s dodging it, even though he doesn’t bother actually moving out of the way properly. It’s just how they interact. The push and pull of their relationship, even this many years down the line.

“Why even bother looking?” Casey asks him, eye to eye now she’s stood in front of him. 

Derek shrugs a little in response, “Something to do, I guess. Did you get through to anyone?”

“They all think we’re idiots. Sarah asked if we’ve run out of gas.”

It’s Derek’s turn to roll his eyes now. It’s not that he doesn’t like Sarah, it’s just that she always assumes he’s an idiot and he’s tired of that bullshit. He’s never really given her reason to not think that to be fair - but also, if you’re going to assume things and never change your opinion on those assumptions, he’s not gonna make an effort to be nice. Even if you are dating his best friend. Plus, he knows Casey’s not particularly fond of her either.

“Sarah can go fuck herself, to be quite honest.”

Casey grins at that, “Bobby’s borrowing his dad’s truck. Says he’ll come get us…”

“There’s a ‘but’ coming here, I can feel it.”

“His dad won’t be home for a couple hours,” she admits with a slight grimace, “And even then he’s a 40 minute drive away from the cabin.”

“Right, so,” Derek sighs, letting his head thump back against the roof of the car with a thud, “We’re stuck for a bit.”

“Guess we are,” Casey says, looking around a little. There are no other cars to be seen in either direction, which isn’t really a surprise. The roads around here have been quiet all week. Every time they’ve ventured out they’ve barely passed any other traffic until they’ve reached the main town - and even then, it’s still not exactly been busy.

The plan was to be in the middle of nowhere, and they’ve truly managed it. There’s eight of them sharing a cabin that can barely sleep six comfortably. It’s hot, and sticky, and the A/C is jittery at best. But they’re by a lake, a mile from the nearest neighbours and surrounded by nature. It’s exactly what they all need before they start their senior year at Queen’s.

“Wanna make out?” 

It’s Derek who asks, raising his head to look at Casey again. Her response could go either way. Sometimes this is something they do, sometimes it’s not. There’s no hard feelings, no matter who’s asking or what the response is. It’s probably something they should talk about at some point, with graduation and the pull of the real world growing ever closer, but those conversations haven’t particularly gone well in the past.

Actually it’s not even that they haven’t gone well, they just outright haven’t happened. They’ve been started - by both parties, at different times - but usually they get… distracted.

Casey tilts her head a little in consideration, “Sure, why not,” she replies as she steps into Derek’s space. His hands find her hips with a practised ease, and she’s got one hand immediately in his hair whilst her other guides his face to where their lips meet with the accuracy of someone who’s done this a million times before.

To be fair, they might have. Casey stopped counting after a while. For the first few months, she’d kept a tally in her diary. No label next to it, just solid vertical lines crossed over in batches of five. No one knew what they meant. 

Well, one person did. When he’d caught a glance over her shoulder in the library one day, Derek realised instantly.

“You’re keeping track?” He’d whispered at her, eyes blown as if outraged but Casey could tell that was a cover. It hadn’t been outrage, it hadn’t even been disbelief, he’d been outright turned on and they both knew it.

She’d stopped counting soon after. When she knew she’d missed a few anyway. When the space she’d allocated for the markings was full. She was reluctant to continue it elsewhere, plus around that time Derek had just started seeing someone, and Casey was in the midst of a fling with one of her dancing partners so the thing between them, whatever it had been, was over. 

Until it wasn’t. And then it was again. And then… well OK. Let’s just say they went round in circles.

They were still going round in circles.

“This is a bad idea,” Casey says against Derek’s lips - her fist is still in his hair, gripped tightly and ready to tug in the way she knows he reacts to most. His hands have found their way to her arse- above her dress still, for now, but they both know it’s a matter of time.

“A pretty good bad idea though,” is his reply. He would move away from her, except she’s the one who has him pinned currently, and he can’t exactly melt himself into the car underneath him, “But we can stop if you want to.”

“Shut up, I meant being outside.”

“Oh.”

She presses herself further into him as she laughs against his neck, nipping there for added effect and a promise of ‘soon’ right as she pulls away, “Get in the car, Der. We’re not scaring the wildlife with our pasty asses.”

“I don’t know, Case,” Derek says as she steps away from him, his hands dropping slowly so he’s still touching her for as long as possible before they get the passenger door open. “Could be a decent show for them.”

Casey wastes no time in pushing the passenger seat back as far as it can go, and dropping it so it’s almost horizontal before falling backwards into the car and lying herself down, “Whatever, just get in here and close the door.”

Normally Derek’s not one for following instructions, but Casey on a mission - especially Casey on a mission which will most likely end in his favourite way - is a Casey he must always obey. He follows her easily, not so much careful about where he’s placing his weight as running on pure instinct by this point. One hand goes straight up her skirt this time, stroking the side of her hip and he’s pleased to feel the light lace which means that maybe, just maybe, she was hoping something like this would happen. The feeling goes straight to his dick and he can’t help but place a searing kiss to her mouth as he leans into her. 

Casey arches her back to meet him as he does, her hands already undoing the buttons on his stupid hispter pants. Zippers are so much easier, but she knows this isn’t just to wind her up: he doesn’t even own any more jeans with zip fastenings. Not after the last pair she accidentally tore a hole through. To be fair, though, there were already rips in them. For fashion, apparently. She’d just made them worse.

“Do you have a condom?” Casey asks, once his dick is in her hand. Which is fairly quick given he apparently wasn’t wearing any underwear today and, wow, does that do something to Casey. Specifically, to her vagina.

Derek stops his current task of leaving a hickey just under the collar of her dress to sit up and laugh a little, “Would you believe me if I said I picked some up at the store?”

This at least causes Casey to pause. Because she does believe him, but she doesn’t want to think too much about the implications of that right now. This is the first time they’ve hooked up in six months, she shouldn’t have been expecting it. This isn’t what they do at the moment.

“Planning on shagging Sarah just to shut her up?” She asks, instead.

“Let’s be honest, Case,” Derek starts as he sits up, “We’ve been one eye fuck away from jumping each other right in front of everyone the last few days.” He’s straddling her hips now as he leans over to the bag of groceries in the back seat to dig out the box in question, “And I’ve definitely been dreaming about climbing into your bed in the middle of the night.”

Casey lets her hands wander down his chest as he talks. The chance of being coy is gone now, totally, and what they’re left with in this moment is the choice of shutting up, or being honest with each other. 

“What if I’d come to you?”

He stops in his movements, “Really ?”

Casey tries not to be affronted by the surprise in his tone, because he may have a point. It’s not that this thing between them is never her suggestion, it’s just that she has a certain way of going about it, and in reality that way does not involve waking him up in the middle of the night with a handjob. Even if it does in her fantasies.

“Yeah,” she says, using the opportunity of his stunned silence to push her hands up underneath his shirt to encourage him to take it off - a motion he dutifully follows as she continues, “I’ve thought about it. Waiting til everyone else is definitely asleep. Sneaking into your room without waking you up until my hand’s already around your cock and I can guide you into me.”

Derek can’t do much more than look down at her after that. He’s aware he’s kneeling up above her, shirtless with his pants undone and his mouth is open and none of this is particularly flattering, but having his step-sister describe one of his favourite fantasies to him without him ever having mentioned it to her before is doing things to him and, for a moment, he finds himself unable to move. 

Casey wriggles a little beneath him, closing her eyes as she arches her back trying to get some sort of friction back between them.

“Come on, Der, or I’m just going to have to sort myself out,” she teases, one of her hands in her own hair and the other moving her skirt out of the way because now they’re here she needs something, goddammit. 

That snaps him back into action, and he quickly goes to grab her hand and move it away from herself. 

“No way, Princess,” Derek says as he shifts himself back and down into the footwell of the car, using his grip on Casey’s hand as leverage to slide her towards him and bring her body to where he wants it to be, “That’s my job.”

Any reply Casey may have to that is cut off by her hiss at his teeth making contact with her clit through the lace of her panties. It’s a hiss of surprise, not pain, and she immediately throws her head back to stare at the roof of her car. Her legs hooking easily over his shoulders as he continues his ministrations: a familiar rhythm of broad tongue strokes up from her vagina and hard sucking at her core.

She’s not usually still wearing underwear when he does this, and she finds the feeling of the material between them adding to her pleasure. Feels her orgasm building inside her much, much quicker than it normally does. She responds in the only way she can: by taking back control.

The gentle squeeze of her thighs on either side of his head is the only warning Derek gets that she’s trying to sit up, followed by the grip of her hand in his hair, again, as she tugs him up and out of the footwell to crash their mouths together. 

“Why,” Casey asks, with their teeth clashing and his swollen lips against her, “Is that so fucking hot ?”

Derek smirks as he moves them back up the chair, lying heavily on top of her between her legs, with one of his hands running slow circles around her entrance - feeling both skin and lace as he goes. He loves it when she swears like this. It’s in a way he doubts anyone else has ever heard, even other people she’s slept with. He just can’t imagine Casey, his Casey, forgetting herself like that with anyone else. No matter what the circumstance. This side of her is all for him, and that has him straining even without a barrier.

“Because I’m magic, that’s why.”

Casey cackles at that, and it's a sound Derek loves even if that’s not something he’d ever admit. It’s indelicate and unpractised and part of that side of her he’s obsessed with.

“Condom. Now.” She demands, the hand still in his hair gripping tightly and her other stroking him as he unwraps the one he’d grabbed from the box before he went down on her.

“Yes, Ma’am,” Derek says as he rolls the condom on, before leaning down to kiss her again with a hunger that wasn’t there before. 

Her hand loosens its grip just a little as she enjoys the moment, before tightening again with a clear instruction: time to go.

She shifts her body beneath him, nudging his dick as she does so, and he reaches down to position himself properly.

“They’ll probably tear,” he points out, referring to the now soaked lace she’s still wearing. 

“Good,” is all Casey replies with as she brings their mouths together again.

The panties are small enough that Derek can move them to the side pretty easily to slide himself into her, and Casey raises her hips to meet him as soon as he starts to move. A tug on his head tells him to pick up the pace, make it quick, and who is he to do anything else but comply.

Later that night, when they’re back at the cabin hanging out with their friends, the stars high in the sky and the sound of crickets in the grass around them, Derek’s eyes will wander to Casey often, and easily. Mostly she won’t even notice as she laughs and jokes with everyone else - Derek’s jacket over her shoulders, her own lace panties still in the pocket - and he’ll find himself thinking: “It was a pretty good bad idea, wasn’t it though.”