A/N: This piece was written for the second round of Slytherin Cabal's Death by Quill 2020 competition and received second place in its round. A million thanks to In Dreams for her beta work and also being wonderful and incredibly helpful. Any remaining errors are my own.

How Thin the Line

Hogwarts School of Witchcraft & Wizardry
Great Hall
23 April 995

"Salazar. So good of you to join us." The voice, delicate and feminine, grated on his nerves in a manner only Helga Hufflepuff was able to get away with.

Ducking into a deep bow to press a kiss to her hand, Salazar returned, "Apologies. The work of a potions master never ends."

He could feel their eyes boring into him, and he didn't have to meet their gazes to know. They'd voted against him.

No matter. It was merely a formality.

To his great displeasure, it was Godric to lean forward, delivering the killing blow. "We have discussed your proposal in depth, Salazar, and we find that the notion is unsustainable." The wizard steepled his fingers beneath his chin, affecting an insincere frown by way of apology. "Without Muggleborns, wizardkind will die out, thus necessitating their education within Hogwarts' fine walls."

Salazar had expected no less. With a dip of his head, he tightened his fist and painted on a severe frown. Through his lashes, he watched a self-satisfied smirk work its way up Gryffindor's cheeks, though Salazar maintained a vigil on the others as they observed his reaction.

It was Rowena, though, that he fixated on.

The ripple over her features; the way her jaw fell slack; the hazy, faraway look in her eyes.

She'd had a vision.

Slipping into Rowena's subconscious was like falling into a familiar bed; he'd been plundering the woman's waking conscience for so long in their shared nights together that she no longer recognised the tells of his entry.

Like a reel, her thoughts played out for him as the rest of the table slipped into mundane discussion.

"There will be a boy, Godric, an orphan, who will seek to tear the wizarding world down." Rowena's voice was low and urgent, eyes shining with tears. "Salazar's direct descendant—my direct descendant. He seeks to—" Her voice broke. "He seeks to subjugate Muggleborns."

The man's face tightened as he sipped from a chalice. A flash of lightning illuminated Rowena's study. "Then he must be stopped—we must not permit anti-Muggle rhetoric to gain a foothold. We will deny Salazar's request and stop him at every juncture."

She sniffled, a rare, undignified display for the stoic woman. "Godric, I'm afraid it's not so simple. I—"

"Does he know of your child?" Godric interrupted, the angles of his face cast in harsh relief against the flames.

Rowena crumpled, tears streaking down her cheeks as she turned away, the hand absently falling protectively to her stomach an unspoken answer. "Godric, I love him—how am I to turn him away? Even knowing—"

Suddenly, Godric's face filled her vision. "Do not let your love of him cloud your vision. You must be strong—think of the child. He would poison her, raise her in hatred." Godric stepped away, impassive. "We'll decline his overtures."

Turning away, Rowena stared over the grounds of Hogwarts. "And what of my relationship with Salazar?"

"The future can be changed by a single event," Godric uttered, a hand on the pommel of his sword as he approached. "We wait, and if necessary, we strike. He is a mortal, and though magic runs in his blood, all mortal men must die." He flicked his gaze up to hers. "Your child will want for nothing."

"Salazar, what say you?"

Helga's voice interrupted him, and he ripped himself out of Rowena's head, heart-pounding fury lancing through his veins. "I apologise, Helga. It appears as though my mind was elsewhere in my disappointment."

He did not miss the way Godric's smile turned razorsharp as Helga resumed explaining a new method of sorting students by way of a talking hat.

Hogwarts School of Witchcraft & Wizardry
Rowena Ravenclaw's Quarters
9 April 995

"Salazar, my love, to where are you leaving at such a late hour?" Rowena roused beside him, her hand splayed across the mattress as sweat cooled on her back.

Love-making, she'd called it.

It felt like a lie.

An imagined ichor clung to him as he threw his legs over the side of the bed. Slipping his arms into his discarded tunic, he turned, pressing a dishonest kiss to her forehead. "Godric wakes early—if I am to make it back to my chambers without detection, I must take my leave."

Softening, Rowena ran her fingers over his cheekbones. Already her fingers were tentative, the passion gone from the touch, tainted by the knowledge she'd obtained from her visions. "Stay. If not for the night, then for a few moments more." She let the fine linen sheet fall away, the moonlight rippling across her breasts with a soft, alluring glow. "I sleep better when you stay."

He leaned back into her momentarily, allowing his lips to flutter over her temple despite the betrayal that roiled in him.

The vision. Godric.

His child.

They were to rip away the last good thing he had before he was to know it. Even now, Rowena's warm body filling the crevices of his, he could feel the chasm between them as though she'd forcefully wrenched herself away.

Legilimency proved that her mind whirred through the possibilities that the child she was carrying would produce the heir that ruined her precious Mudbloods.

How thin the line was between love and loathing.

Affecting a disappointed air, Salazar leveraged himself upright, summoning his cloak with a quick wave of his wand. From its depths, he retrieved a potion, mottled purple with flecks of starlight dancing within its depths. "A potion of my own creation; you will sleep without interruption." He tipped her face up to his, planting a kiss to her lips as the lie fell from his. "Until tomorrow, my love."

Unstoppering the potion, Rowena lifted it to her mouth, the bob of her throat confirming her swallow, and Salazar left her, turmoil rioting in his mind as she raised the covering to her chest, her fingers coiling into it.

Slipping through the door of her chambers, he waited, shrouded in the darkness as the night settled around him. Only when he was sure that Rowena had fallen into a deep sleep did he depart.

Through the halls, he stalked, ignoring the distant sounds of students out of their beds reverberating on the stone. Each step punctuated his retreat until he threw the doors open and stormed into the dark, Disapparating as soon as he reached the perimeter of the school grounds.

Capelulo, Wales
Near Nant Ddaear-y-Llwynog
9 April 995

The alehouse was dark around him, lanterns burning low in the hazy air, but he paid the creatures dancing in the shadows no mind. Salazar had no desire for a cheap harlot, not when answers were worth their weight in currency.

And the women here didn't dabble in matters so trivial as gold.

The being he sought ducked into the building on a deceptive zephyr, slipping between the tables as though she were half in the next world already. She didn't pause to order a drink but weaved effortlessly toward him until she stood before his table, violet eyes peering out from beneath her hood.

"What is your name?" Throaty and melodic, her voice was a siren's call to any wizard who lacked fortification of mind.

A trick of her trade, then. A name for her secrets. "Salazar Slytherin. Pureblood." Tipping his head to the bench seat opposite him, he added, "I did not know your kind could walk among mortals."

"Aileana. Though you may know me by other names." She lifted her head, a razorsharp smile flashing in the low light. "And you would do well to address the Queen of the Fairies with respect, Salazar. Particularly when asking for a favour."

His lip curled into a snarl. "Is that a threat?"

The creature was unphased, staring him down. "It is a promise." Her body sat coiled against the wooden grain, her perusal thousands of tiny knives delving into his skin and burying beneath the surface as her fae magic roiled against his. "Your reputation of disdain for 'lesser folk' precedes you," she accused. "Why have you requested my audience outside of the Unseelie Court?"

Drumming his fingertips over the pockmarked surface of the table, he leaned forward. "What do you know of maledictuses?"

The fairy's eyes flashed, a cruel smile working up her lips. "It's old magic. Dark magic." Her lips seemed to drip poison as she lifted her chin. "Fairy magic."

Salazar didn't permit the excitement he felt to colour his face. "Tell me how it works."

She canted her head to the side as she considered him. "The common understanding is that it is a blood curse, passed from mother to daughter via blood." Considering him, she continued, "Though I'm sure you have exhausted common knowledge and found it wanting or you would not have summoned me."

"Although there are no recorded instances, could the initial curse be inflicted on a man at his behest?" Notching an eyebrow, he reached into the depths of his robes, withdrawing a vial of dark substance. "And if I were to tell you that I could pay you handsomely to obtain your services, would you perform the ritual?"

Attention locked on the vial, she reached forward, sharp-nailed fingertips scratching along his palm as she lifted the vial and tilted it towards the light, admiring the contents. Deeming them satisfactory, she pocketed the offering. "It's not often that a wizard offers his own blood in exchange for fairy magic."

He refused to drop his gaze from the fairy's. "I find myself in a rather unconventional position; the blood is powerful—my lineage is pure and magic strong. It can be used in all manner of rituals, but I find that I will need an additional memory alteration spell in addition to the curse." At her sharp nod, he breathed, "How will the malediction take root?"

Studying him, her eyes flashed. "There is no ritual. Akin to your peoples' curses, it will alter your very essence; your lifespan will increase, and you will take on the physical qualities of the being." Her throat bobbed. "It is not your magic's transfiguration—it is a curse, the kind of dark charm that we fair folk excel in. Once it has been performed, it cannot be undone, and it will be nearly immediate. You will have a fortnight to arrange your affairs."

Steeling his spine, he pinned the fairy to the spot. "Fairies cannot lie." The statement came out with an air of inquiry, and Aileana permitted a nod. "Will it affect offspring which have already been conceived?"

Aileana wasn't quick enough to hide the surprise that flashed in her gaze. "If the child was conceived before the curse takes root, it is not likely to be transmitted." The fairy tilted her head, studying him. "Although I cannot deal in absolutes; I have never performed this magic on a mortal."

Fear struck, low and quick, in his core, but he smothered it. It would be a small price to pay to ensure his legacy carried on—that someday, the boy Rowena saw in her vision would finish his work. He leaned forward, offering her his hand with a jerky nod. "Do we have an accord?"

She dipped her head, but not quick enough that he missed the sharp tips of her fangs glint in her smile. "It appears that we do." Her hand rested in his palm, the inky coils of her magic wrapping around his, seeping into the meat of his skin. "This will be painful—try not to scream and attract attention." A feral hunger lit her gaze as they locked eyes. "Any requests?"

Heart racing at the future he was securing, Salazar allowed a rare smile. "A basilisk. I will be a basilisk."

Hogwarts School of Witchcraft & Wizardry
Chamber of Secrets
23 April 995

Dank air cloaked him, a film of moisture coating his skin so thick he thought he might never be clean of it.

Far above him, a single shaft of light illuminated the floor around him, the rest of the low green light only cut through by the magic emitted by the strong arcs of his wand. "Partum Obice. Cave Inimicum." Each charm layered overtop the previous, weaving into a seamless arc.

The Chamber of Secrets. He'd landed on the name after the motivations which drove him to such measures.

A home for his secrets. For Rowena's secrets.

Wooden pillars arched grandly to the towering ceiling, a grand facade to welcome his descendant upon his entrance. In a fit of grandeur, he'd carved his likeness into the stone, the mouth of which opened into his bedchambers, for which he'd have little use in short order.

Her echoing footsteps announced her presence long before she arrived, having followed him upon his exit of her chambers.

"What have you done?" The accusation lanced through him. Rowena stood on the threshold of the tunnels in her navy dressing gown, hair artfully cascading over her shoulders.

"Rowena, welcome. I had hoped curiosity would outweigh your self-preservation. It appears we defined the house virtues aptly." He turned then, gesturing at the hall carved out around them. At his image in the stone. "The Heir of Slytherin will be welcomed home."

Instantly, Rowena recoiled. "You knew." Her lower lip trembled, tears shining in her eyes even as she lifted her wand carefully. "For how long?"

On silent feet, he glided towards her. "You're not adept at guarding your mind, Rowena. For as intelligent as you are, you're a terrible Occlumens." He wrenched through her mind with a sharp tug, pulling memories of her vision to the forefront of her mind with a sneer. "When were you going to tell me of our child?"

Horror flitted over her features. "Soon. We were to be together." Her hand smoothed over her stomach, cradling a nonexistent swell. "We were to be a family."

Salazar reached her, lifting a hand to run over the smooth marble of her features as he rifled through her mind carelessly. Her jaw spasmed in his grasp, the grind of her teeth audible. "One change," he whispered, leaning into her with a lover's embrace. "One shift is all it takes to change the future forever."

He stepped out of her embrace, gesturing to the cavern around him. "My greatest achievement. Because of your betrayal, I will safeguard my lineage and my legacy. I will ensure that Mudbloods no longer taint these hallowed walls."

Rowena backed away, her wand raising between them in a shaky hand as she wrapped the other protectively over her abdomen. "Salazar, think about what you are saying. All magic is good, regardless of blood purity."

Sneering, he approached her. "They steal our magic, and they desecrate our ancestry with their inferiority. They're a plague on wizardkind, Rowena. Can't you see?"

Tears clouded her eyes, a single streak falling prettily over her sculpted cheekbones. "You can't do this, Salazar. Godric and Helga, they will know if you hurt me."

A disbelieving laugh gusted from his cheeks as he crowded her, cupping her cheeks. "If I hurt you? You lied to me, tried to hide my child from me, tried to change me." Gooseflesh sprang to life on her cheeks as he rubbed his thumbs over them. "I'll not hurt you. No, I would never."

She wilted into him in relief for a half a moment before her eyes flashed, her wand snapping up a moment too late. "Fli—"

"Imobulus!" She slumped into his arms, wand clattering to the ground as he cradled her to his chest and rose, carefully ascending through the tunnels in which they had arrived. "I hate to charm away the memories, but I simply cannot have you thwarting this."

The castle was quiet, even the few portraits dotting the walls seeming to slumber peacefully in their frames, and as he walked through the castle with Rowena curled into his chest, Salazar mourned their relationship.

That he'd never know his child, and that she would never know her power as the descendant of Rowena Ravenclaw and Salazar Slytherin.

But ridding Hogwarts of the blight that was Mudbloods… it was a task he would see to completion one way or another.

Salazar found the familiar worn stone that led to Rowena's chambers, shifting the witch to one side and waving his wand over it in the series of complicated arcs he'd seen her perform before.

His heart clenched painfully in his chest when he entered the room for the last time and laid her atop her bed, tear tracks staining her porcelain skin. "Don't cry, my love," he whispered, lips brushing over her temple. "We all must make sacrifices for the greater good."

Lifting his wand, he whispered the incantation his blood had earned him from Aileana, replacing Rowena's memories of the Chamber with a night spent in his arms.

A goodbye, even if she wouldn't have thought so at the time.

As her eyes turned fuzzy and she aimed an absent smile at him, he tilted another Dreamless Sleep potion to her lips, encouraging her eyes closed.

Heavy-hearted, he arranged her beneath the covers, lingering on the gentle swell of her abdomen, and he turned jerkily, summoning a quill and parchment as his skin began to mottle, scales rising to the surface of his skin.

Quickly, then, before he returned to the Chamber.

To await his heir's arrival.

My Dearest Rowena,

It is with my sincerest regret that I pen this missive. When you awaken, I will have gone—please do not try to find me. I fear that our differences conflict on a fundamental level, and it would be selfish of me to ensnare you in the endless rancour characteristic of my tenure here should I be forced into proximity with Godric—I fear his disdain has already soured our love.

I will remember you fondly.

With all my love,

Salazar