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A Nest of Vipers

Summary:

Una Montague, a sharp-witted and ambitious seventh-year Slytherin, reigning as the Head Girl, is haunted by a dark incident from her past: the near-fatal entrapment of her brother, Graham Montague, in the vanishing cabinet during his fifth year by someone in Dumbedore's Army.

Determined to unravel the truth and enact revenge, Una embarks on a perilous investigation, delving into the intricate web of Hogwarts' alliances and enmities. Her quest is complicated by the unexpected involvement of Cormac McLaggen, a handsome yet arrogant seventh-year Gryffindor. Despite the warnings from his friends about Una and her notorious Slytherin clique, known as 'The Vipers', Cormac finds himself falling for Una. And she, him.

Una and Cormac's romance is a treacherous one, as they navigate through a maze of secret relationships and moral dilemmas. Can love truly bridge the divide between two seemingly incompatible worlds? Or is it merely lust that exists between them? As the line between good and evil blur, Cormac and Una must make choices that set off a butterfly effect, defining the future of the wizarding world.

Notes:

Dear god, please forgive me for what I wrote while ovulating. First time writing an OFC but I think it's still as hot as reader-insert. OFC and McLaggen are both 18. Also I just want to say that I fucking hate JK Rowling and am gleefully bastardising her work.

(See the end of the work for more notes.)

Chapter 1: Smudge

Chapter Text

The Slytherin common door shut with a thundering echo. Una Montague looked up from her Astronomy homework and locked eyes with Meredith Prewett. Uh-oh.

Professor McGonagall had asked Sabine to stay behind after Transfiguration that day and judging by the way her high heels stomped across the stone as she stormed towards the group of sixth-years sitting by the fire, it had not gone well.

“You’re in my seat,” said Sabine Zabini with a cutting glare. 

Pansy Parkinson sprang up without argument. “Sorry Sabine. Let’s go,” she added to her friends who hastily packed up their things and made themselves scarce.

Una and Meredith rushed over from the little alcove at the lake window as Sabine sank into the onyx wing-backed chair with a woeful groan.

“Sab, are you okay?” fawned Meredith, perching on the arm of Sabine’s chair. 

“If I ever see that old hag again, it’ll be too soon,” she hissed. 

Una sat down on the hard marble table in front of them. “What did she want?” she asked. When McGonagall had asked her to stay behind, Sabine had told Una to go on without her, and so had she made her way down to the dungeons and found Meredith studying in the common room.

“She told me if I want to sit my Transfiguration N.E.W.T., I’d have to start taking remedial Transfiguration lessons with her.”

“No!” gasped Meredith. Una didn’t say anything. She knew from sitting beside Sabine all throughout the previous year that she was lucky to have even made it to seventh-year Transfiguration. But the first few weeks of term had made it apparent that she was not keeping up with the curriculum. 

“Well, of course, I told her where she could stick her remedial Transfiguration.”

“You didn’t!” said Meredith. Sabine caught Una’s eyes before rolling hers.

“Of course, I didn’t, Meredith. No, I thanked her very much for the kind offer but told her I’m withdrawing from the class. Obviously.”

Oh, Sab,” Una groaned. “You should have just done a few extra lessons with her.”

“Ugh, as if.”

“Who am I going to make fun of her hideous hat with now?” Una smirked, trying to hide her excitement and Sabine returned it. There was one person in Transfiguration who didn’t have a partner and Una was already making silent plans to sit next to him.

Cormac McLaggen. Tall, stupidly beautiful, beautifully stupid Cormac McLaggen. God, she wanted him. But Slytherins and Gryffindors barely spoke to each other here unless completely necessary in lessons. Both houses liked to think they were the others’ opposite. But Una knew that they were simply two sides of the same coin. 

Cormac barely even looked at Una. And for some reason that made Una want him more. 

When she, Sabine and Meredith walked down the corridor arm-in-arm, boys - even the Gryffindors - couldn’t help but stare. Slack-jawed, awestruck, terrified by the trio’s powerful feminine energy. But not Cormac. He was head and shoulders taller than the three of them so he didn’t even need to avert his gaze - he just simply looked over them as if they weren’t there.

Sabine and Meredith (but especially Sabine) would be horrified if they knew about Una’s crush. Sure, he was good looking but it would be social suicide to date a Gryffindor. Even one as well-connected as him - apparently his uncle was extremely high-up in the Ministry.

Una had a stupid habit of wanting what she couldn’t have. And, fuck, she was desperate to have him.

Her parents wanted her to be with someone from a pure-blood family. But it’s not like she wanted to marry Cormac or anything. She just wanted to fuck him. Even just once. Just to find out what he’d be like. He was so big and broad and downright intimidating. But Una was sure she could have him whimpering, begging for her-

“Hello? Earth to Head Girl?” Sabine and Meredith looked at her expectantly. Una blinked a few times and shook her head.

“Sorry - I was thinking about… Transfiguration. What were you saying?”

“Who are you going to sit beside tomorrow?” asked Meredith.

“Ugh, I don’t know.” Una made a show of rolling her eyes. “I’ll probably just sit at the back by myself. I’ll get a lot more work done without you there,” she teased Sabine.

“You’re such a goody-two-shoes,” said Sabine, pulling her long, black braids over her shoulder. “Whatever are you going to do without me leading you astray?”

It wasn’t so much a question of what, thought Una, but who.


A bag landed on Cormac McLaggen’s desk with a thud and he looked up in surprise to see Una Montague perched on the edge of the desk, looking down at him. “You’re good at Transfiguration, right?” she asked abruptly.

He furrowed his eyebrows together. “Me?”

“Yeah, you. Can I sit here?”

What fresh hell was this? What was one of the Vipers doing sitting on his desk? It was rare to see any of them alone. Cormac looked behind her sceptically. “Where’s your friend?”

Sighing heavily, Una pulled her bag back onto her shoulder. “I’ll sit somewhere else.” 

She turned to walk away, swishing her hair as she went. But before she took a step he said quickly, “Wait - yeah, you can sit here.” He supposed it would be poor manners to let a pretty girl, albeit a notoriously mean one, sit by herself at the back of the class when there was a perfectly good empty seat next to him.

“Only if I’m not inconveniencing you.” 

Already feeling like he was about to regret it, he gestured to the seat.

Cormac continued to look unsurely at her as she slid into the seat next to him. “What happened to Sabine?”

Una rummaged in her bag. Cormac expected her to take out her textbook but instead, she withdrew a small, black compact mirror and some lipgloss. “Oh, she dropped Transfiguration...” Cormac watched quietly as the lipgloss wand drew across her lips, spreading a shimmering pink glaze over them. And for some reason, he felt like he should look away. Like he was watching something extremely private. But he didn’t. He couldn’t. “She couldn’t handle it.” 

She pressed her lips together and pouted a little in the mirror, examining her neat work. The way she preened herself made Cormac want to reach out and smear the gloss over her face, just to see her reaction.

She snapped the compact shut and jolted him out of his daze with a start. 

“I should give you two for flinching,” she smirked. 

Professor McGonagall strode past them to the front of the class and the chattering students quietened down. She announced that they were going to be working on conjuring birds today.

“Might I remind you that your N.E.W.Ts are only a few months away and none of you are yet to successfully conjure more than a feather.”

The class groaned and got to work, trying with limited success to conjure birds using the Avis spell.

“Why is this so bloody difficult,” grumbled Cormac after some time, concentrating on his wand tip while Una lazily brushed a comb through her hair - her wand abandoned on the table. “Conjuring inanimate objects? Fine. But birds…”

“Have a lot of trouble with birds, then?”

“Oh, very funny.”

“I’m serious. I’ve never even seen you with a girl.”

Cormac lowered his wand and turned in his chair slightly. Oh, so this was why she sat here, was it? He couldn’t deny she was good-looking. But still, a Slytherin.

“Oh yeah, been watching me, have you?”

“I’m just very observant.”

“I’m single if that’s what you’re asking?”

Una rolled her eyes. “You wish, Cormac.”

Cormac leaned back in his chair and looked her over, resting his arm on the backrest as he did.

“What about you?”

“What about me?” she asked innocently, putting her brush in her bag before raising her wand and pretending to concentrate on conjuring birds.

“I’ve never seen you with anyone. Except for the Vipers. Or is that a thruple situation?”

“The Vipers?”

“You know, Slytherin’s other monsters. Sabine and Meredith.”

Una laughed. He had half-expected a shrill cackle. But her laugh was warm, even genuine. “Oh, so is that what they’re calling us in Gryffindor Tower?

He shrugs. 

“It’s catchy.”

“So? Are you?”

She too lowered her wand and leaned in closer to him. “Are you asking if we fuck each other?” she murmured, staring intently into his green eyes. “Are you picturing me rolling around in the sheets with them in the Slytherin girls dorm? Making them moan my name?” she teased.

Cormac paused and swallowed. “What if I am?” he said, and was pleased when it sounded more confident than he felt. They were both playing with Fiendfyre, talking like this so brazenly in the classroom. But he wasn’t sure who was more skilled in this Dark Art.

“I should slap you,” Una said, moving closer still so he could hear her barely audible admonishment. He felt her bare leg in her stupidly short skirt pressing against his.

“Don’t. I can only get so hard.”

Her eyelashes dipped as she looked down at his lap. Una drew a sharp inhale when his fingers twitched suddenly towards his belt.

He smirked.

“I was joking. But I should give you two for flinching.”

Uno looked up again at him coolly. “You’re not gonna give anything to me.”

“Oh yeah?” He gave her an arrogant smile as if he found it hard to believe. “Why’s that?”

“First of all, I’m not that easy. And second of all, I wouldn’t be caught dead dating a Gryffindor.”

“Who said anything about dating? What if  -”

“Miss Montague, Mr McLaggen. Is there something amusing you’d like to share with the rest of us?”

Silence fell over the class again and Una and Cormac turned hastily in their seats to face the front.

“I was just explaining the theory, Professor” Una said sweetly, seemingly unphased by the interruption.

“Then perhaps you could demonstrate?” Professor McGonagall challenged, calling her bluff.

Una pointed her wand and out shot six yellow twittering canaries.

McGonagall’s lips pursed together in a thin line. Cormac was sure she was about to award Una points but instead she addressed him. “And Mr McLaggen?”

Cormac extended his own wand. A stream of feathers erupted from the end and floated down onto the floor. Una bit her lips, trying to stifle a snicker at his expense.

Any further embarrassment on his part was saved when the bell rang signalling the end of class and McGonagall dismissed them.

“I suppose I’ll see you on Friday?” asked Una casually, positioning her bag on her shoulder.

“Thursday.”

“The next lesson’s not 'til Friday.”

“Slughorn’s dinner thing. You’re not ditching it again, are you?”

“I don’t know… Sabine and Meredith say it’s a waste of time, sucking up to an old has-been like Slughorn.”

“They don’t need to come.”

“Trying to get me alone, Cormac?”

Cormac laughed. “It might just be nice for you to make some new friends. You’re not that bad when you’ve slithered away from the Viper’s nest.”

Una narrowed her eyes. “I happen to like my current friends, thank you very much.”

“Sure but I only meant  -”

“Believe it or not, I don’t actually care what anyone from your house thinks of me or my friends. If you’ll excuse me, I need to get back to my thruple.”

And with that, Cormac watched as Una strutted out of the classroom, leaving him to kick himself for managing to fumble the quaffle so hard - right when it was going his way too.


“Did you miss me terribly, Una?” cooed Sabine when Una found her and Meredith beside the common room fire that afternoon.

“It was the worst,” she said, plopping herself down on the sofa, watching the way the fire danced against the green tiles. “McGonagall picked on me and didn’t even give me a measly point for doing the Avis spell correctly. And nonverbally I might add.”

“Typical,” said Meredith. “It’s so unfair. She hates us.”

“Who did you end up sitting next to?” asked Sabine, flicking through her magazine.

“Erm, that guy… McLaggen,” said Una, as if his name was of little consequence.

“Not that oaf.”

“I know,” said Una. “And it’s not like I could even copy him - he was about as useful as a chocolate cauldron. I’m surprised he’s not in remedial Transfiguration.”

Sabine laughed but Meredith paused thoughtfully.

“He is quite handsome though, isn’t he? And rich, I think.”

Eugh, Meredith. You have terrible taste,” said Sabine.

Una quickly copied Sabine’s look of disgust while Meredith backtracked.

“I just meant he’s alright to look at. Still a Gryffindor though, obviously.”

“And an idiot. Didn’t you hear how he ended up in the hospital wing last year? Eddie Carmichael dared him to eat Doxy Eggs for a bet. Some Head Boy he is, Una. Between him and McLaggen, you’ll have your work cut out for you this year.”

Una wrinkled her nose.

“Poor Una,” said Meredith sympathetically.

“I did find out some good gossip though,” said Una raising her eyebrows and leaning back on the sofa. “The Gryffindors call the three of us The Vipers.

“That’s rude,” said Meredith but Sabine shrieked in a fit of giggles.

“I love it!” she laughed. “We really are just living in their heads, aren’t we?”

Una grinned. “I know.”

Sabine closed her magazine and stood up. “Let’s go down to the Great Hall. I’m starving. What do vipers eat anyway?”

“If they’re anything like Ashwinders then insects. Raw eggs,” said Meredith in an attempt to be helpful.

“That’s disgusting, Meredith,” said Sabine, linking her arm through Una’s. Meredith hurriedly latched on to her other side. 

“Speaking of dinner,” Una said. “I’m thinking about going to Slughorn’s on Thursday.”

“Ugh, pass,” said Meredith.

“Why?” asked Sabine, giving Una a shrewd look. “Blaise said it was terribly boring.”

“I know but I probably ought to as Head Girl. Bit of a snub if I don’t go twice. And maybe it’ll help my marks in potions.”

“You reckon?” asked Meredith.

“Well, it can’t hurt my marks if he likes me.”

“That’s a good point,” said Sabine thoughtfully. “Alright, I’ll come too then. I need all the help I can get since I’ve got one less N.E.W.T. this year.”

“Yeah, me too.”

Shit, thought Una. 


Blaise Zabini was waiting in the common on Thursday night when Sabine, Una and Meredith finally ascended from the girl’s dormitory.

“Mum was complaining you’ve not written to her yet,” he told Sabine.

“I’ve been busy.”

“All four N.E.W.Ts proving to be time consuming, then?”

“Shut up.”

The four of them made their way along to Professor Slughorn’s office. They opened the door to find several plush seats already occupied around the extravagantly decorated table. Una felt irked when she noticed McLaggen was notably absent. This whole thing really would have been a waste of time if he didn’t turn up after all.

“Welcome, welcome!” Boomed Professor Slughorn. “So nice of you to join us. Blaise, good to see you again - and you’ve brought your sister!”

“Yes, sir. Thank you for inviting me,” said Sabine graciously as they found their seats and Slughorn beamed. Sabine had such a way of making people feel flattered, even special just from her presence. 

“And our Head Girl, Miss Montague. And Miss Prewett! I taught your father, you know.”

“Yes, sir. He spoke extremely highly of you,” said Meredith, sitting down.

Una sat on Sabine’s right, leaving a few seats next to her empty. Just in case, said a small voice in her head.

Slughorn began introducing everyone. Una was surprised to notice the way Blaise’s eyes lingered on a fifth-year girl, Ginny Weasley. Though she wasn’t sure if it was distaste or something entirely opposite. Interesting. Una didn’t say anything - she just made a mental note of it, the way she so often did with snippets of potentially damning information.

Slughorn’s office door opened again and Una looked to see Eddie Carmichael entering. Her heart sank as she turned back around again.

“You could have held it open,” said Cormac McLaggen’s voice. Una froze, not daring to glance at the door, incase Sabine noticed her constant fidgeting in her seat.

“Sorry, mate,” said Eddie, pulling out the free seat beside Una.

Cormac slid into the open chair before Eddie could. “That’s more like it, cheers mate.” He looked at Una. “Alright? - ouch!” 

Eddie slapped the back of Cormac’s head before sitting down on his other side. Cormac ran his hand through his dark, curly blonde hair.

Idiots,” scoffed Sabine under her breath.

And Una had to agree. 

Cormac shuffled his seat in closer to the table. His shoulders were so broad that Una could feel his arm pressing up against her. Even if she folded her arms, she could still feel him, taking up far too much space.

As the evening went on, they listened to Slughorn regale stories of all the famous students he had taught, each of them members of what he called his ‘Slug Club’. Every time he said the name it made Una cringe. He fawned over Cormac, asking him about his uncle’s Ministry connections, praised Meredith’s dad’s apparent Potions prowess as a youth and asked Sabine and Blaise what their famous mother was up to. He asked Una about her father - a prominent benefactor of St Mungo's - but was more interested in Una's Head Girl duties. And Una was pleased about this. The less she had to talk about St Mungo's the better. 

After dinner, Slughorn summoned a bottle of Elf-made wine with a flourish of his wand. “Just for those who are of age,” he chided the younger students in a sing-song voice, “And only a glass each. Or else you’ll need an Awakening Draught tomorrow!” He chuckled. “And speaking of which - “ Slughorn looked at the seventh-years mischievously, “- you’d do well to brush up on that ahead of our lesson on Monday.”

Sabine grinned at Una and Meredith. It had been worth enduring the evening after all, if they were getting tips about the following class.

As Una drank her glass of wine, she felt Cormac’s leg brush against hers. Maybe the wine had emboldened her but she didn’t shrink away. Instead, she shifted slightly, leaning her leg against his. 

On Una’s left, Sabine and Blaise began sniping at each other again when Blaise suggested that their mother might send her a howler. On her right, Cormac was telling Eddie about his plans to try out for the Gryffindor Quidditch team. 

Una lifted her glass to her lips but paused when she felt something. A large, warm hand grazing her bare leg. Cormac’s. She looked down but her lap was covered by the tablecloth. 

She moved in closer to the table and Cormac made to withdraw his hand when he felt her shift but she placed her own hand firmly on top of his, before returning hers to the table.

Cormac continued talking to Eddie as if nothing had happened while Una felt his hand trail further up her leg and under her skirt. She took another sip of wine and pretended to listen interestedly as Slughorn started waxing lyrical about a friend he had who was writing a biography about a Vampire.

“I simply must introduce you to Eldred Woprle, Miss Carrow. He has a lot of contacts at the Daily Prophet, you know.”

Una felt blood rushing below her waist as Cormac’s fingertips traced across her inner thigh. Her own hand gripped her wine glass with more force than was necessarily required, just for something to keep herself steady.

“I was sort of hoping Potter would be here tonight. It’d be good to get him on side before tryouts.”

“I don’t know why you’re arsed, mate. I keep telling you - football. Now that’s a real game.”

The plush, cozy room now felt stiflingly hot. Adrenaline coursed through Una’s body as she shakily raised her glass to her lips to try and hide her face. Cormac’s hand skirted over the crux of her thigh. Wine met her lips as she tilted her glass, letting the fruity, slightly sour liquid infiltrate her mouth.

“Well maybe I’ll tell Mum that you’ve got detention with Flitwick already - then we’ll see who gets a howler.”

Una’s heart raced in her chest. The several conversations going on in the room turned to white noise. Slowly, carefully, so as not to brush against Sabine, Una moved her legs apart. A silent invitation. She breathed shakily as she felt Cormac’s fingertips slip under the hem of her soaking wet underwear.

“My my!” cried Slughorn suddenly, causing Una to flinch and inhale an entire mouthful of wine. “Look at the time!” Cormac quickly removed his hand as Una began choking and spluttering.

Sabine gave her a concerned look as she coughed. “Are you alright? You’re bright red.”

Una wiped her lips, trying to compose herself quickly. “I’m - I’m fine,” she gasped. “Just went down the wrong way. And wine makes my cheeks flush.” She extracted her compact mirror and lipgloss, re-applying it hastily.

“It’s gone straight to your face too, mate,” said Eddie Carmichael, looking at Cormac. 

Cormac laughed and touched his hand to his warm face. He cleared his throat. “Yeah, yeah, I suppose it does a bit.” 

Una looked at him and felt herself flush even deeper when she saw him press two fingers thoughtfully against his lips. They were wet.

“Oh, how time flies when you’re having fun. You’d all better be off back to your dormitories. And if Mr Filch gives you any trouble, you just send him straight to me,” said Slughorn, waving his hand in the air.

“Let’s get out of here,” said Sabine, standing up abruptly.

Una pushed her chair back and followed her, Meredith and Blaise out of the room without so much of a backwards look.

As soon as they got out into the corridor, Meredith laughed.

“What a drag that was. Honestly, it would be worth failing Potions if I never had to endure that again.”

“I know,” agreed Sabine.

“I think I preferred it to another evening with Malfoy and the rest,” scoffed Blaise. “They’re always brooding these days. And I suppose the wine wasn’t too bad. If you don’t choke on it, that is.”

Hilarious,” said Una.

“What did you think, Una? You were unusually quiet.”

Una’s abdomen tingled. Her brain worked overtime to come up with an excuse while blood rushed in her ears.

“Well, I had you lot squabbling on my left and two idiots on my right talking non-stop about Quidditch.” Una rolled her eyes convincingly. “But it wasn’t too dreadful. At least we know what’s coming up in Potions on Monday.”

“Well, that’s it sorted then. You can go with Blaise next time and report back to Meredith and I if Slughorn gives us any more hints,” said Sabine, with finality. 

Una mulled this over, pursing her lips together thoughtfully. It certainly would be easier to talk to Cormac McLaggen if she only had one person keeping an eye on her. She could hardly just be expected to talk to Blaise and only Blaise all night. She was allowed to network, right? And perhaps, she thought, Blaise would like to network with Ginny Weasley.

“Fine,” said Una. “But you owe me. Big time.”

Sabine linked her arms between Una and Meridith as they sauntered along the corridor to the dungeons. Una still felt faintly embarrassed about her unseemly choking display. With her free arm, she searched for her mirror in her tiny handbag, wondering if she had any wine down her front.

“Shit,” said Una, stopping and the four of them halted. “I think I left my compact.”

Meredith groaned. “I’m not going back in there. If I have to hear anything else about Vampires-”

“It’s fine - go ahead. I’ll see you two in the dormitory. See you later, Blaise.”

Una untangled herself, turned on her heels and passed the last few stragglers leaving Slughorn’s dinner party.

Her heels clicked as she walked back up the deserted corridor and around the corner.

“Forget something?”

Cormac McLaggen was sitting on a window ledge in the dark hallway, checking himself out in Una’s little black mirror. He snapped it shut and hoisted himself off the stone ledge, walking towards her.

Una extended her palm expectantly.

“What’s the magic word?” he asked, standing in front of her. Una looked up at him as he towered over her. He was so tall she had to strain - her face was only at eye level with his chest.

Avada Kedavra?” suggested Una, attempting to snatch the compact from his hands but he reacted quickly, pulling it out of her reach.

“Ooh, not quite,” he grinned.

She took a step towards him, their chests almost touching as she looked up at him through her lashes. “Please, Cormac?”

He hadn’t expected her to surrender so quickly. Cormac grudgingly gave her the compact back and they stared at each other for a few moments, neither of them daring to address what had just happened in Slughorn’s office.

“You know, that lipgloss is very pretty,” he said, curling two fingers under Una’s chin. Her heart pounded in her chest again as she looked up into his strikingly green eyes. His own lips were rosy, tinged slightly pink from drinking the same wine. “Too pretty.”

Cormac took his thumb and slowly dragged it across her bottom lip, smearing it down her chin. He squeezed her face roughly and Una smacked his hand away, scowling.

“There. That’s better.” He gave her an arrogant look. “See you tomorrow.”

Una let out a scoff of disbelief as Cormac walked away, leaving her standing alone in the corridor. 

She opened her compact and examined herself in the mirror - a pink, glittering streak was smudged across her chin and there were faint red marks from where he squeezed her face.

He was right, she thought as she looked at her slightly dishevelled appearance, she did look better like this.