'Cora,' Derek's quiet voice rang through the loft.

'Derek,' Cora answered calmly.

Derek kept his eyes on his book. 'Where are you going?'

'Out.' Cora said inching a step closer to the door.

'Out where?' Derek calmly turned the page.

'Outside,' Cora said sarcastically. Derek glared at her retreating form and then went back to his book, flicking back to where he'd lost his attention, around the same time he heard Cora squirting perfume. It was eleven thirty, and Cora never went out during daylight if she could help it.

Shaking his head Derek returned to the copy of The Scarlet Letter Jennifer had left behind yesterday.

It happened again on Tuesday, Cora left at exactly the same time although on Wednesday she was working out furiously. Derek had finished The Scarlet Letter and was considering texting Jennifer for something else when his sister fell into a push up position.

'Not out today?' Derek asked casually resting his elbows on his knees.

'Nope,' she answered after an obvious pause.

'You're doing that wrong,' Derek said. Cora pushed a harsh breath out of her mouth and went back to her push ups. 'You're going to hurt your shoulders.'

'So what I'll heal!' Cora snapped.

Derek shrugged and left the loft. He was hungry and he didn't fancy sticking around Cora's grumpy mood. He didn't miss the irony in that thought at all.

On Thursday's Jennifer took a night class so Derek didn't see her. Normally he found plenty to distract himself with but the sight of Cora in the shortest skirt ever caught his attention. 'Going somewhere?' He asked.

Cora startled and turned to glare at him. 'To the mall with Allison and Lydia.' Cora said.

'Be careful of those two,' Derek said eying her skirt. 'Isn't it cold out?'

'That's how dad used to talk to Laura,' Cora said sadly.

'Do you need money?' Derek said changing the subject gently.

'He never said that,' Cora admitted as Derek dragged some bills from his wallet.

'Call me if you need anything,' Derek said catching a whiff of perfume.

'Done pine for Jenny too much,' Cora grinned and Derek tried not to act like the grumpy old man he felt he was turning into.

On Saturday morning Derek woke with a start. He had no idea what did it; he just lay still as Jennifer shifted minutely into her pillow. Derek pushed the duvet around her shoulder and that's when he noticed it, Cora creeping out. She was halfway across the floor of the loft and moving at a snail's pace.

Derek kept half an eye on her, shifting gently to slide his arm across Jennifer's back. Jennifer made a noise and Cora froze. Derek couldn't keep his smirk off his face, especially when she started to move again. She was half out the door when Derek spoke.

'Have a nice day,' he offered wrapping his arm around Jennifer so his palm rested between her breasts, her heartbeat catching the edge of his hand. Cora stilled, and then moved like a flash and Derek wondered where the hell she was going at five in the morning but he was too comfortable to care right now.

On Sunday everybody descended on Derek's loft, each bringing with them some sort of food or beverage. Derek was on his bed relaxing with a newspaper when they arrived. Jennifer was curled at his side, some marking spread out, but she was more interested in reading the paper with him.

'Who's idea was this I wonder?' Derek said quietly. Jennifer looked up at him and he kissed her head as the kids fawned over his couch and television. They drew straws as to what movie they should watch. Isaac's choice won; Final Destination.

Derek shot him a look and noticed Cora wedged between him and Stiles. Stiles was sitting ramrod straight, and Cora was keeping her distance too it seemed as Scott bounced over to the bed. 'Are you going to watch the movie?' He asked with a smile. 'Hey did I get an A?'

'I liked your arguments and how you managed to relate them to present day politics, very clever indeed.' Jennifer said like a proud mother hen. She already made Derek read Scott's essay and Derek was forced to concede that it stood out.

Derek rolled his eyes and glanced back at the couch. Cora had moved away from Stiles, sitting at the other end from him but she still looked miserable. Derek decided he'd have a word.

Monday before lunch Derek hung around the parking lot as Cora slipped out the door. She started walking and Derek kept a good distance between them. He was confused when he realised she was heading to the school. By the time he caught up she was straddling one of the bleacher benches and chatting to Stiles. Derek watched her steal some of the boy's lunch but he couldn't get much closer, he didn't want her to know he'd followed her.

The same thing happened the rest of the week, Derek found her with Stiles at the bleachers. He didn't follow her on Friday because he was busy trying to make a quarterly budget for the family, but when Cora declined the movies with him Derek narrowed his eyes.

He followed her again, this time to the old theatre in town where the sweet popcorn was best and they liked to show old movies rather than new ones. It was Derek's favourite place to bring Jennifer. He watched as Stiles appeared and she pecked his cheek. Stiles blushed but he bought their tickets and their candy. Derek bought one ticket and slid into the theatre, sitting back. Stiles had his arm resting on the back of Cora's seat and eventually she rested her head on his shoulder, when the little sleezeball dropped his arm around her.

Eyes narrowed, Derek spent the rest of the movie glaring at the back of Stiles's head willing him to turn around so Derek could flash red eyes at him but it didn't happen. They left the theatre and Derek followed slowly, his cell phone buzzing in his pocket.

Asshole, your dinners in the oven if you want it but don't you dare wake me!

'Fuck!' Derek hissed rushing home. Sure enough there was a delicious smell lingering and Jennifer's back was to him. Derek figured he should eat then join her in bed; perhaps she'd be offended if he didn't eat it.

'Jenny baby,' Derek whispered as he crept beneath the duvet.

'Don't Jenny baby me, I'm asleep,' Jennifer hissed.

'You're talking to me,' Derek pointed out. He got no reply but he curled around her all the same. Now he needed to work out what to do about his little sister.

He was almost asleep when he realised she hadn't come home. At all.

Derek found them on Saturday afternoon deep in the preserve, and for a long moment he was confused before he realised Cora was trying to teach Stiles to fight.

'It's not like Xbox, you can't just hold a button to give you more power, and you have to put that power in your own body with practice!' Cora said. 'Also layers.'

'Hey its cold here and I like my layers, I'll probably have them on if I run into a fight anyway.' Stiles complained.

'Humour me baby, take them off,' Cora said.

'No. Why?' Stiles asked affronted.

'Because I want to objectify your body that's why,' Cora tugged on Stiles's hoodie. Derek watched him struggle out of his layers leaving him only in a crude shirt. He reached for Cora who batted his hands away.

'As if, now assume your position.' Cora said.

'You're so dirty!' Stiles leered but Cora had him on the ground and Stiles was yelping for mercy so Derek figured he'd leave them alone for now.

The loft was empty when he got back; Jennifer's weekend bag was missing. Derek groaned and sank into the couch.

'Are vampires real?' Isaac asked tilting his head towards Derek.

'No.' Derek answered tapping his fingers against the table.

'Wow Derek that song describes you!' Scott said. AC DCs Night Prowler was playing out of the iPod Allison of all people had patiently taught him to use.

'Because we watched Twilight and then we got reading about the myths-'

'Who are we?' Derek interrupted Isaac. Scott blushed and looked away. Allison was scribbling notes from a book not listening.

'The three of us,' Isaac said. 'And Scott's mom.'

Derek snorted and shook his head. His phone was quiet, neither Cora nor Jennifer was replying to his texts. 'Where's Stiles?' Derek asked Scott.

'I have no idea,' Scott lied checking his watch.

Derek hummed and went back to drumming.

'When you were a kid what did you want to be when you grew up?' Another stupid question came from Isaac.

'Someone who was lucky enough not to be surrounded by a bunch of idiots.' Derek said.

'I want to design clothes, like practical but pretty clothes that can conceal weapons.' Allison looked up and Derek forced himself not to be afraid of the hunter who was tentatively becoming one of his allies.

'Hey we better go,' Scott said and they started to pack up their things.

'Where to?' Derek asked.

'We're going bowling.' Isaac said wrapping a scarf around his neck.

'I haven't been bowling in years,' Derek grinned remembering the time he broke a ball with his strength. He had to tell Paige it was faulty craftsmanship. Was that really the last time he was bowling?

'It's kind of a date thing,' Scott said with wide frantic eyes.

Cut Derek nodded. He didn't intend to tag along; he had other plans but the knowledge that they didn't want him there hurt more than he was willing to admit. 'See you around,' Derek said, listening to Allison chastise Scott as they left.

'What was I supposed to say?' Scott yelped. Derek waited fifteen minutes or so before grabbing his keys and a copy of To Kill a Mockingbird.

Sure enough the rusty old jeep belonging to Stiles Stilinski was haphazardly parked close to the door. Derek parked at the back of the parking lot and slunk low in his seat. The book had been one Jennifer studied from in high school so it held her scent well.

Derek sent her another text and half an hour later got a reply saying girl's night out.

So he settled to watch for his sister and try to figure out her game.

It took hours, but the kids spilled out of the place in one big pack. The twins were there too, with Danny and Lydia, Scott carrying Allison on his back while Isaac argued about something with Stiles. Stiles who had one arm draped around Cora's shoulders, their fingers tangled together.

They paused to say their goodbyes and parted ways, Stiles leading Cora to the jeep, where he backed her into the side of it and lowered his face. Cora caught him and spun them, her hands fisted in his shirt. Stiles was smiling and leaning down and he spun them back, stepping impossibly closer to Cora and just when Derek's fingers curled around the door handle to move and save her his phone rang.

Derek snatched his eyes down to his phone. Jennifer was calling him. Derek snarled but he answered the phone whit a grumpy 'what!'

'Derek,' Jennifer sounded like she was crying.

'What's wrong?' Derek asked.

'I think one of my friends has been drugged, can you come help us?' Jennifer pleaded.

Derek shot a look at Stiles who was still trying it on with Cora but he knew his sister could handle herself. 'Where are you?' He asked Jennifer as he started the car.

Cora didn't come home on Saturday night either which was probably a good thing considering the makeup sex he and Jennifer indulged in. On Sunday morning she tried to make Derek go to her place and get her clothes but Derek liked the idea of her having to wear either his clothes or nothing at all so he refused in what was probably a dick move but right now he didn't care because Cora was marching through the loft like she hadn't been AWOL since Friday.

'Who are you?' Derek asked with a frown. She didn't smell of sex but that meant nothing because of showers. She did smell like Stiles though and he'd get Stiles had a bit of her scent on his skin.

'You should take up comedy for a living, you're so hilarious!' Cora said climbing the stairs. Jennifer glanced at Derek from beneath the blankets. Derek rolled over the top of her.

'She's dating Stiles.' Derek said.

'Imagine the kids,' Jennifer teased. Derek glared down at her for a second narrowing his eyes as she tugged his hair. 'I think they make a cute couple.'

Derek grunted. 'I don't understand why she hasn't told me,' Derek said.

'Perhaps it's a secret and they want to make it work.' Jennifer pointed out.

'They all went bowling last night, even the twins.' Derek said. 'That's where I was when you called.'

'Watching a bunch of teenagers, creepy much?' Jennifer asked.

'Looking out for my baby sister.' Derek corrected.

'Leave it, they'll tell, you in their own time.' Jennifer said as Cora came back done the stairs. Derek checked over his shoulder but she didn't say goodbye.

'I'm sure,' Derek wasn't convinced. They'd probably tell him on the wedding invitations, if they invited him.

'Know what I fancy?' Jennifer said tugging Derek's shoulder.

'What?' Derek asked gently.

'Well I've never tried rimming,' Jennifer said making circles on his skin with her nail.

'You've never rimmed or been rimmed?' Derek asked.

Jennifer raised a saucy eyebrow. 'Both,' she said.

'Let's go shower!' Derek grinned dragging her from the bed.

Three weeks later and Cora was still sneaking around. The pack eluded him, keeping their secrets close to their chests and barely involving him in anything. They used the loft less and less and it grew quiet, and Derek found himself glad of even Peter's company from time to time.

Cora slept in her room on week nights but she took herself away for long weekends at a time. Derek didn't want to be the monster to confront her, didn't want to intimidate Stiles but it seemed as if that's what they expected from him and that hurt.

Rebuilding his relationship wasn't easy but the secrets were worse, much more hurtful than any cruel words. Jennifer wanted to talk to the kids, and sometimes Derek caught Allison giving him sad looks he didn't understand but he ignored all of that, formulating a plan in his head himself.

It was late and dark, a Monday night. The boys room smelt fresh, like it had been cleaned recently but Cora's scent lingered underneath, Cora's and Stiles, they fit well together Derek realised happily. He wanted that, he was happy for them but gutted that they wouldn't share their happiness.

Derek made himself comfortable, noticed some of Cora's things here, fresh clothes, a book half under Stiles's bed, pages of scribbled notes. Was Cora studying with him too, was she missing an education? Derek felt bad, but he had asked her those types of questions and she refused to answer them. Was she confiding in Stiles what she wouldn't confide in Derek.

The sound of voices downstairs caught Derek's attention. The sheriff was heading out for night shift, asking after Cora, saying goodnight and sleep well. Derek slunk into the corner, an easy growl coming from his throat. Stiles bounded into his room and tossed his bag and coat into the darkness, flipping his lamp, frowning when it didn't come on.

He turned to catch the main light when Derek made sure he could see Derek's eyes, his red alpha eyes.

'Uh,' but Derek stepped forward catching his collar and slamming him into the wall.

'My sister?' Derek's voice was deceptively calm. If he wanted a monster he would get one.

'Derek, old buddy old pal,' Stiles licked his lips and met Derek's eyes.

'My little sister?' Derek asked leaning closer. Stiles's eyes flicked over his face. Derek waited. He was hurt by the lack of respect he'd been shower when he'd been so open and honest with all the kids about Jennifer because he didn't want them to feel weird about Derek screwing around with their favourite teacher. Derek had used those very words to Stiles.

'I can explain,' Stiles bit his lip. Derek raised an eyebrow. 'Okay not sitting down in a well light place with large objects between us?'

'Stiles!' Derek snarled.

'Okay, okay,' Stiles said holding his hands up. 'It wasn't real at first, Cora was helping me out because I liked somebody else, but then I realised I liked her, more than liked her, so we started dating.'

'Why didn't you tell me?' Derek finally stepped back.

'Uh, duh, because you hate me and you'd rip my throat out!' Stiles blathered fixing his clothes.

'Don't you think if you told me rather than me finding out then that would have been better for your throat?' Derek asked with a raised eyebrow, but Stiles wouldn't see it in the dark.

'Dude all you do is intimidate us, I mean you stare at her all the fucking time, and Scott too, it creeps us out. You're all grumpy and don't want approached, you glare at Isaac when he asks you questions and get exasperated with me when I have good ideas. You listen to Cora because she's your sister and Allison because you have some twisted friendship going in there. You won't look at Lydia or the twins and you side eyed Danny that one time the guy came over and now he won't come back!' Stiles stopped and took a breath. Derek nodded and turned away from him, heading out the door.

'You're welcome any time in my loft, you and your girlfriend. You can even stay and I'll do my best not to look at anybody so they feel more comfortable.' Derek said stepping into the hallway.

'Derek don't be so butt hurt by all of this,' Stiles said following him. Derek ignored and trotted down the stairs. 'Derek?'

'What?'

'Why do you stare at Cora and Scott, Ms Blake, you watch her too, why?' Stiles asked.

Derek examined the back of the door and sucked his bottom lip. 'Because you're all there, with me.'

Stiles didn't speak again as Derek left, but when he got home Cora was sitting on the couch. 'So some of us are lost with Game of Thrones and we were going to marathon it this week, but only Stiles and Jennifer have read the books, so I was hoping we could all watch it here and catch each other up,' Cora said.

'I've read them too,' Derek sank onto the couch. Cora lay back and kicked her feet onto his lap.

'I love you, you know that right?' Cora said.

'Do you love Stiles?' Derek asked.

'Mom used to say Hales fell in love too easy, I never knew what she meant until I met Stiles.' Cora said.

'You love him?' Derek asked.

'He doesn't love me,' Cora said sadly. Derek ran a hand over her shin.

'I think you're wrong, I like Stiles, just, don't tell him I said that. And don't let him be an asshole.' Derek said with a half-smile.

'Oh I won't.' Cora said with a grin.

Derek's loft was full of teenagers, one excitable English teacher and sheriff Stilinski. 'My mom's on her way!' Scott said coming through the door.

'Dad said Peter invited him?' Allison asked Derek.

Derek rolled his eyes. Hard. And it hurt, especially when the two men in question walked through the door without a care in the world. Derek tucked himself in the middle of the pack and proceeded to be the worst host ever, resting himself between Jennifer and Stiles, ignoring the fact that his little sister was practically on top of Stiles.

Derek closed his eyes and took a deep breath as the sheriff questioned Stiles and Jennifer on the opening sequences and Peter gave his own analysis. It was going to be a long Saturday.