Full Summary: The Order fights a losing battle. There is a traitor among them who is fixated on killing them off. One by one they fall, like chessmen being brushed aside. The lone Slytherin is naturally suspected, even by the ones she thought she could trust. But even as war looms upon their doorsteps, happiness can still be found in the cottage Vivian now calls home…until, of course, someone from her past returns with information that could change the tide of battle, tragedy strikes, and the world that she has built for herself comes crashing down within a matter of days. A new purpose rises from the ashes, and with it comes a new Vivian Blair, who must learn to live without the ones she has come to love.

Welcome to Regimentum, the second installment of Vivicendium. As usual, a few things to note before you begin reading:

Some creative license will be taken with regard to the canon timeline in this story, as is hinted below. This is to lay down the foundations for the next installment of the series.

Most of the characters and plots that were left unfinished in Season 1 will be carried over to Season 2, including OC characters. It is recommended to read Vivicendium first in order to gain context.

This first chapter is a flash-forward scene that will connect to the center of this story. Then, as in Vivicendium, the story will move backwards in time. Regimentum will focus heavily on the First Wizarding War, the Order of the Phoenix, and Regulus's plot, which will have more significance in the second half of this story.

This story is rated M due to potentially graphic scenes of death, torture, and the overall consequences of war, as well as scenes of a sexual nature. Chapter warnings will be included.

Disclaimer even though the word 'fanfiction' is a disclaimer in itself: I do not own Harry Potter.

I will be updating this story every Sunday.

I hope you all enjoy and I look forward to hearing everyone's thoughts :)

Chapter One | Auspicium melioris aevi

[An omen of a better time]

There is something irresistibly sweet in the darkness. Something that calls to her in the night. It is like wind rattling the windows on a stormy evening, impossible to ignore. She feels it wrap around her every thought, tainting as it goes, destroying with its icy fingers. It is a blank expanse that stretches beyond her vision, so far that it seems to cover everything in sight; every sentiment, every belief, everything that Vivian Blair is and was and will be, to the point where it is almost impossible to recall the parts of herself that ought to be there. The pieces of her soul that ought to be breathed in flame and happiness.

"You need to close your mind," he tells her, but it is not such an easy thing to do, when memory blossoms behind her eyes and turns them glassy with anguish, and the ice comes to rattle upon thought and consequence and leaves her gasping in the wake of it.

"I'm trying," she hoarsely responds. Her fingers dig into the upholstered armchair, nails scratching against the polished wood. She sees him there in her mind's eye, so vivid that it's unnerving. He is smiling at her from the corner of a photograph, dressed for once with certain care as he lifts a goblet and toasts to the happiness of their friends. He is there again, hair splayed over pillows, reaching for her with a laugh and pulling her into the warmth. And there again, concern etched within his eyes as he takes her hand and pulls her back, away from ricocheting spells and blasts of green light – and again, and again, and again, her name upon his lips, calling out with love and anger, accusing eyes and arresting smiles; a tormenting conundrum that had not been rectified, could not be rectified, until…

"Enough, that's enough," she gasps, slamming her head so hard against the back of the chair that stars swim momentarily through her vision. She wrenches her eyes open and sees a face studying her with a careful expression, just emotionless enough to showcase the barest hint of Regulus Black's own anguish.

"Your mind is still too weak," he tells her. His voice is bathed not with judgement, but with cautious concern. The iron of his eyes is softened in the dim light of the study. He shifts them away from hers as though it is difficult to look at her directly. "…I'll give you a few minutes to collect yourself," he murmurs, and strides to the fireplace to lean against the mantle. He stares into the flames that dance within the hearth.

Vivian doesn't respond. She merely sits there and clenches down upon the arms of the chair, knuckles blanched a stark, bone-white. The veins of her neck protrude from the effort it takes to compose her emotions, but the ice has melted somewhat and a burning fire has alighted in the back of her throat. She tries to swallow it down, but her mouth is too dry and it feels as though there is ash upon her tongue; memories taken out of place and stripped down, like a photograph sitting upon a sunny windowsill for so long that the faces within it fade into the background.

"Perhaps we should pick this up tomorrow night," she finally croaks into the thickening silence.

How much farther will he press her? This is an agonizing torment.

Regulus turns to look at her. His expression, which is always so calm, now pulls itself into a frown.

"You've hardly made any progress at all," he says, "and we've been at it for weeks."

Vivian bites down upon her inner cheek and scratchily responds, "What does it matter? Who cares if anyone sees my memories?"

His frown deepens. In an instant, Regulus has turned to face her and is crossing the room to return to her side. He kneels down in front of her chair and reaches for her hands, pulling them into his cold grasp. "You know why this is important, Vivian. We both know that He'll be back one day, and when He returns…"

Slytherins. They are ready for everything. Despite being one herself, Vivian has nearly forgotten the way their minds work. She has spent so much time around Gryffindors that it is almost chilling to be in Regulus's presence once again.

With a tight swallow, Vivian draws in a shaky breath and squeezes his hands. "Okay. Once more."

Regulus stares at her closely for several long moments before nodding. "Once more," he agrees, and stands up to lift his wand.

Vivian straightens in the chair, returns her hands to the armrest, and closes her eyes. She takes several deep breaths, trying to empty her mind, to compose her thoughts, to press them into order. Regulus waits for her to nod, but even though she thinks she's ready, she isn't.

"Legilimens," he murmurs, and at once they both tumble right back into memory better left alone.

There he is again, standing before her and pushing her hair back. She can almost feel his fingers running over her scalp, gentle and calming even as he chuckles at her.

"What are you trying to do, kill every plant in England?" he snorts. "Just accept the fact that you're awful at gardening, Godric. Honestly, how you passed herbology, I'll never know."

"Shove off, you mutt," her voice responds, light and amused even as she pushes him.

"Mutt?! How dare you," comes his laughing response, and then he is dragging her into him and she's laughingly pushing him back as a warm summer breeze pushes through the valley that spans out around them…

Her heart is shaking. The vision of the garden vanishes.

"Vivian," he murmurs into the night, "look at me."

He reaches for her, eyes swept over with worry and sadness. "Look at me," he whispers, trying to turn her towards him. His fingertips brush against wet cheeks.

"There was nothing you could do," he tells her, and pulls her into his arms as the oppressing darkness weighs upon them, and the thin light of the moon and stars struggle to broach the curtains…

Her heart shakes again.

"Harden your mind," Regulus's voice tells her, "imagine that there is a sheet of ice covering your thoughts."

But she can't, she can't, she can't.

A dimly lit pub unfurls before her mind's eye. She sees herself laughing as if she has not a care in the world, shucked against Sirius as he playfully nudges Peter.

"I feel like I haven't seen you in ages, Pete," Sirius says.

"Yeah, where've you been?" James asks, his fingers entwined with Lily's on the table's surface. "Have you been holed up with some bird?"

Peter coughs into his butterbeer and frowns, "Why, would it amuse you if I was? Only my mum would love me, is that right?"

Vivian sees James blink in surprise. Peter's hostile tone makes the rest of the table quiet down. She sees herself peering carefully at him from around Sirius's figure, but she could never have known…

"That's – look, I never actually meant – " but James's spluttering only makes Peter stand up and grab his coat.

"I'll see you all at the next meeting," Peter mumbles, and scurries for the door before James can call him back. The rest of them turn to stare at each other awkwardly, none of them knowing what to say. But then…

"The war's getting to him," Remus placates, "he's just stressed out. We all are."

Lily squeezes James's hand. Their matching wedding bands gleam in the dim light of the fading sunlight. Her voice is tentative when she suggests, "Maybe we should all get together for dinner soon? It's been a while…Peter probably feels a bit disconnected from us…"

James shrugs and looks over at Sirius, who shrugs back at him. "You can all come over to the cottage," he proposes, casting a glance at Vivian. The edge of his mouth tilts up. "But you may want to bring your own food."

Vivian huffs at him as James laughs, "Still eating take-out every night? Set another dishcloth on fire lately, Pride?"

Vivian glowers at him. "Shut it, Potter. It happened one time."

They all laugh, and her heart shakes again…

"Vivian," Regulus sighs, "you need to try harder."

But Vivian can only snap, "I am trying, Reg," as another scene unfurls before her.

Sirius has her pressed to the mattress. Sirius is kissing his way over her neck. Sirius is fumbling with the buttons of her shirt, whispering her name with a sigh, covering her mouth with his, pressing his body against hers…

"I don't want you to see that," Vivian angrily heaves, trying to push him out of her mind. This time, Regulus makes it easy for her, because he doesn't particularly want to see it either. He lifts his wand and runs a hand through his hair, but his moment of weakness is only a moment; a mask, carefully void of emotion, quickly replaces it.

"If I wanted to, I could look into your thoughts about the Order, find out Dumbledore's weaknesses, gather information to destroy it once and for all…" Regulus catches her eye solemnly. "If I wanted to, I could see everything, because you aren't even trying to keep me out."

Vivian clenches her jaw and, through gritted teeth, says, "I told you, I am trying."

Regulus lifts his wand again, and she braces herself. He says, "Try again," and she does. But it is hard, when Sirius's face unravels before her, smiling in the way that would always make her heart so warm. It is hard, when a part of her wants to cling to his memory, which has since been tainted with mugshots and insane laughter, haunting her every step.

"He's so small," Sirius breathes. His eyes are full of wonder. The bundle in his arms coos quietly and reaches up to slap a tiny hand over his jaw. Vivian leans over Sirius's shoulder and takes the hand, marveling at the little fingers. In the bed some paces away, Lily watches with a tired smile.

"What did you decide to name him?" Sirius asks, his voice still captured with wonder.

James proudly responds, "Harry."

Harry, Harry…where is he now? She should have taken him in…but perhaps James and Lily wouldn't have wanted her to…perhaps they really didn't trust her after all…

"Who else have you been seeing behind my back?" Sirius angrily demands. "Who else?"

"You don't understand, Sirius, I – "

"I can't believe you've hidden this from me," he snarls.

"You know why I did," she says. "I knew you would react like this."

"Doesn't trust mean anything to you? Don't you see how this looks to the other members? He's one of them, Vivian. You're cavorting with the enemy!"

"Sirius, please listen to me, let me explain – "

"Enough," Vivian gasps, forcing her eyes open again, "Stop, stop, Regulus, stop."

This is too painful. This is too much for one soul to take.

"Stop," she whispers, even though Regulus has already lowered his wand. But the memories still unspool from her mind's eye, unraveling as if they are a film and she is an unwilling audience. She sees Sirius throw her hand from his arm and turn towards his motorbike.

"I need some air," he had said; the last sentence he's ever said.

Vivian thinks she needs some air right about now, too. She throws herself from the upholstered chair and, chest heaving, croaks, "I'll be outside. In the garden. I need a moment." Before she's even done speaking, she's rushing towards the study door and throwing it open, without care of the late hour or the people sleeping on the next floor. Sirius's last words pluck at every thought, invade every corner of her mind, color every emotion that lurches haphazardly through her. She feels as though she can't breathe.

When at last she tears the back door open, she gasps into the night sky. She feels shaky, without substance. She closes her eyes against the cold air and sinks down to bury her fingers into the dirt, as if she thinks that by clinging to the earth, perhaps she might resettle her mind, and lock her memories into iron cages.

But they keep unspooling, they keep unraveling. She is on a collision course and there is no path but the one directly ahead, which leads into the darkness and reaches out with icy fingers to capture her. The chill is almost pleasant, but she is still resisting its call, trying to grasp onto the pieces of herself that still survive.

But the memories continue with their torment, always:

I need some air, he had said, and then he vanished in the night.