The fourth floor classroom at six in the morning was cold enough that their breath showed.
Mia didn't mind the cold anymore. Three weeks of early mornings had recalibrated her sense of what was reasonable, which was either personal growth or evidence of Bellatrix's corrupting influence depending on how you looked at it.
"Again," Bellatrix said.
Mia raised her wand and cast the same shield she'd been casting for forty minutes. It came up solid and clean and Bellatrix hit it with something sharp and it held.
"Better," Bellatrix said. "But you're still anchoring it to your wand hand. When your wand hand is compromised—"
"The shield fails. I know."
"So stop doing it."
"I'm not doing it on purpose."
"I know. That's why we're doing this until it stops being something you do." She raised her own wand. "Again. And this time when I take your wand hand—"
"You're going to take my wand hand?"
"I'm going to attempt to take your wand hand," Bellatrix said, with the patient precision of someone who had explained this before. "The shield should hold regardless. If it does you can have breakfast. If it doesn't—"
"We go again."
"We go again."
Mia rolled her shoulder and reset her stance. Bellatrix moved without warning — not the spell she'd been throwing for forty minutes but something lateral, a binding hex aimed at Mia's wrist. Mia sidestepped, felt the shield flicker as her focus split between movement and casting—
The shield held.
Barely. But it held.
Bellatrix lowered her wand. Something in her expression shifted — the same almost-pleased look she got when something met the standard she'd set for it.
"Breakfast," she said.
"Finally." Mia lowered her wand and flexed her fingers. "For the record I would like to note that six in the morning is an objectively unreasonable hour."
"For the record," Bellatrix said, already packing her bag, "you've improved more in three weeks than most people improve in a year. The hour is working."
"That's the nicest thing you've ever said to me."
"I've said considerably nicer things to you."
"About my spellwork specifically."
Bellatrix paused. Looked at her with the morning light coming through the high windows and the familiar expression — fond and dry and underneath both of those, warm. "You're good," she said. "You were good before. You're becoming exceptional."
Mia looked at her for a moment. "Was that difficult to say."
"Somewhat," Bellatrix admitted. "You're very smug about compliments."
"I'm appropriately pleased by them."
"You're smug." She held the door. "Come on. If we're late to breakfast Narcissa will have eaten all the good pastries."
April moved through the castle with the particular energy of a term heading toward its end — N.E.W.T. pressure building, the days getting longer, the grounds full of students trying to study in the sudden April warmth. The Slytherin common room had settled into the new shape of things: Mia and Bellatrix no longer performing indifference, Avery no longer pretending to be neutral, the Horcrux work invisible underneath everything but present in the way the three of them occupied the same orbit.
Rodolphus had been quiet since the corridor confrontation.
Not gone — Mia could feel the shape of him in the background, the particular quality of someone reconsidering their approach. He came to meals. He was civil when proximity required it. He watched, which he'd always done, but differently now. Less like someone building a case. More like someone waiting.
It was Avery who noticed first.
"He's been having conversations," he said one morning, appearing beside Mia on the way to Charms. Quiet, casual, the information delivery they'd developed over months. "Not the usual people. Younger students. Second and third years."
Mia kept walking. "Which ones."
"The ones with family connections to the Dark Lord's known sympathisers." He paused. "He's recruiting."
"For Voldemort or for himself."
"Does it matter."
"It matters for how we respond," Mia said. "If he's building a personal network inside the school he's dangerous in one way. If he's building it for Voldemort he's a proxy, which means the problem is larger but also more legible."
Avery was quiet for a moment. "Both," he said. "I think both. He's useful to Voldemort and he knows it. He's making himself more useful."
"By building a school network."
"Hogwarts is going to matter in the next few years," Avery said. "In ways people aren't thinking about yet." He glanced at her. "You know that."
"Yes," she said. "I do."
He peeled off toward his own class and Mia walked the rest of the way to Charms turning the information over in her mind like a stone with something underneath it.
She told Bellatrix at lunch.
Bellatrix listened with her fork halfway to her mouth and then set it down very deliberately.
"He's building inside the school," she said.
"That's what Avery thinks."
"Avery is usually right about things he notices." She looked at the table. "Which means we need to be doing the same thing."
"We have Avery. Narcissa. Andromeda."
"We have three people. He's working on a network." She looked at Mia. "We need more."
"Carefully."
"Obviously carefully." She picked up her fork again. "There are people in this school who are going to be facing a choice in two or three years. The earlier they understand what they're choosing between—"
"The better chance they have of choosing right," Mia finished. She paused. "Sirius."
Bellatrix looked at her.
"He's going to fight," Mia said. "In my timeline he spent twelve years in Azkaban for it. He's already—" She glanced across the hall to the Gryffindor table where Sirius was engaged in what appeared to be a highly animated argument with James Potter involving a lot of wand gesturing. "He's already halfway there. He just doesn't have a direction yet."
"He's my cousin," Bellatrix said. "And he's fifteen and he makes everything chaotic."
"He organised six suits of armour into a coordinated formation for us last term."
"That's not—" She stopped. "That's actually a reasonable point." She looked at Sirius across the hall. Something complicated moved through her expression. "Later," she said. "After the N.E.W.T.s. He doesn't need this on top of his O.W.L.s."
"Agreed." Mia paused. "There's also the question of what Rodolphus is telling the younger years. If he's shaping how they see things before we have a chance—"
"Then we need to be in those conversations too." Bellatrix was quiet for a moment. "Not directly. Not obviously. But present." She looked at Mia. "This is what the shadow war looks like. Not just the Horcruxes. This."
"Yes," Mia said.
They ate in silence for a moment.
"The training," Bellatrix said. "We need to extend it. Not just spellwork." She looked at Mia directly. "Legilimency."
Mia looked at her. "You want to teach me Legilimency."
"I want to teach you Occlumency first. Then Legilimency." She held her gaze. "Against Voldemort every other skill we have is irrelevant if he can walk through our minds whenever he chooses."
"Occlumency means you'd be in my head," Mia said.
"To teach it effectively, yes." A pause. "If that's—"
"It's not a problem," Mia said. "I trust you." She paused. "I just want you to know what you're walking into."
"I know what I'm walking into," Bellatrix said. "Your mind is extraordinary and probably terrifying and I've wanted to see it properly since August."
Mia looked at her.
Bellatrix held her gaze with complete composure and the faintest suggestion of a smile.
"Tomorrow morning," she said. "We start Occlumency."
Occlumency was harder than anything they'd done so far.
Not technically — Mia understood the theory, had read everything Bellatrix had given her, knew what she was supposed to be doing. The difficulty was the doing of it, which was entirely different from understanding it.
Legilimency, Bellatrix had explained, wasn't reading thoughts. It was reading the emotional landscape underneath thoughts — the shape of what mattered, the texture of what was true.
"When I enter," she said, standing across from Mia in the fourth floor classroom, wand down, "you'll feel it as pressure. Your instinct will be to push back against it. That's wrong. Pushing back creates friction and friction creates openings." She paused. "You want to present a surface. Not a wall — walls have edges you can get around. A surface. Smooth. Reflective. Nothing to catch on."
"How."
"Find something simple. A fact. An equation. The exact wording of a piece of text you've memorised. Hold it in the front of your mind and let everything else fall back behind it."
"And you'll be able to tell if it's working."
"Immediately." She looked at her steadily. "I'm not going to go deep. I'm just going to test the surface. You'll know when I'm there."
"Okay," Mia said. "Go."
The moment Bellatrix entered her mind was unlike anything she'd experienced.
It wasn't painful — more like a sudden awareness of being observed from inside, a presence that was distinctly not her own moving through the edges of her thoughts. It was disconcertingly intimate. She felt her defences scramble and scatter and the surface she'd been trying to hold dissolved immediately.
Images rose without her permission — the Department of Mysteries, the light, the field in August rain. Bellatrix's hand extending. The library. The summer. The ring warm on her finger.
Bellatrix withdrew.
The room came back.
Mia let out a breath. "That was—"
"Your defences are non-existent," Bellatrix said. Her voice was slightly different — careful in a way that said she'd seen something and was deciding how to handle it. "Which is normal for a first attempt. The instinct to scatter is almost universal." She paused. "You were thinking about August."
"I noticed."
"It's the formative memory. The mind returns to what shaped it." She looked at Mia steadily. "It's not a weakness. It's just information."
"What did you see."
"The field. You arriving." A pause. "Me."
They looked at each other.
"How did I look," Mia said. "To you. That night."
Bellatrix was quiet for a moment. "Lost," she said. "And furious about being lost. And—" She stopped.
"And?"
"Extraordinary," she said quietly. "You looked extraordinary. Even bleeding in the rain on my family's lawn."
Mia looked at her across the classroom.
"Tomorrow," she said, "I'll build a better surface."
"You will," Bellatrix agreed. "It takes time. Don't be frustrated with the first session."
"I'm not frustrated." She paused. "How deep did you go."
"Not deep at all. I barely touched the surface and you scattered." She tilted her head. "You have a lot of memory in the immediate layer. The war. Seven years of—" She stopped again. "A great deal of loss."
"Yes," Mia said simply.
Bellatrix looked at her. The professional assessment was still there but underneath it something quieter and more careful.
"We don't have to go further than you're comfortable with," she said. "The Occlumency can be practiced without—"
"I know." Mia met her eyes. "I'm not worried about what you'll see. I told you everything on the lake in August."
"Telling and seeing are different."
"I know that too." She held her gaze. "I trust you with it."
Bellatrix was still for a moment. Then she nodded once — the small, certain nod that meant she'd received something and was keeping it.
"Again tomorrow," she said.
"Again tomorrow," Mia agreed.
Three weeks later the Dark Marks began appearing.
Not on skin yet. In the common room — in the way people carried themselves, in the conversations that stopped when Mia walked past, in the particular quality of the room after a weekend when certain people came back different.
Rosier was first.
He came back from a Saturday away and sat in the common room that evening with his left arm slightly protected and his eyes slightly bright and the composed expression of someone who had done something irrevocable and had decided to be fine with it.
Mia looked at him from across the room.
He looked back, level and careful.
Nothing was said.
Mulciber the following week. Then two others whose names she knew but hadn't tracked closely.
The common room divided in the way Bellatrix had predicted — not dramatically, not with confrontation, just a gradual and definitive rearrangement of who sat near whom and what conversations happened where.
Bellatrix watched it from the seventh year end of the room with the expression of someone observing something she'd known was coming for years and still found difficult to watch.
"Four," she said one evening, low enough for only Mia to hear.
"That we know of," Mia said.
"That we know of." She paused. "He's going to send for me."
"Yes."
"Soon."
"Probably."
They were sitting close enough that their shoulders touched and the fire was warm and the common room was full and complicated around them.
"When he does," Bellatrix said, "I'll need to have a reason. Something that explains why I haven't come without sounding like refusal."
"The N.E.W.T.s."
"After N.E.W.T.s he'll have no patience for academic excuses."
"A family obligation," Mia said. "Something Arcturus requires. He understands family obligation — he uses it himself. If I make the right approach to Arcturus—"
"My grandfather will play along if I ask him correctly," Bellatrix said. "He's not going to follow Voldemort." A pause. "He thinks he's managing a situation. He doesn't understand yet what can't be managed."
"Will he understand eventually."
Bellatrix was quiet for a moment. "I don't know," she said honestly. "He's very old and very certain. Those things are hard to shift." She looked at the fire. "But he signed the contract. He did that knowing what it meant."
"He did," Mia said.
They sat with the fire and the divided common room and the weight of what was coming and didn't speak for a while. Avery was across the room reading with the focused quiet of someone very deliberately not being marked.
Narcissa came in from the girls' dormitory and glanced across at them and then at the marked side of the room and then back at them with an expression that was fifteen years old and already doing the calculation correctly.
She sat down at the table nearest Mia and opened a book.
Nobody commented.
Nobody needed to.
The Voldemort message arrived on a Wednesday.
Not a letter — a person. A seventh year from Hufflepuff who looked profoundly uncomfortable delivering it and handed Bellatrix a sealed note in the corridor outside Transfiguration and walked away very quickly.
Bellatrix looked at the seal. Didn't open it immediately. Put it in her robes and went to class.
She opened it that evening in Mia's presence, which was deliberate — she handed it across without comment and let Mia read it.
It was brief. The kind of brief that didn't need to be long because the name at the bottom did all the necessary work.
Miss Black — your gifts are known to me. Your time, I trust, is now your own. I look forward to knowing you better.
No signature but the mark at the bottom. The snake and skull, small and precise, pressed into the wax.
Mia looked at it for a moment. Then she folded it and handed it back.
"He's patient," she said.
"He's confident," Bellatrix said. "He thinks patience is a courtesy he's extending because he can afford it." She looked at the note. "He doesn't actually believe I'll refuse."
"Can you write back."
"I have to write back. Not responding is a refusal." She turned the note over in her hands. "I'll tell him I'm honoured. That my family obligations require my attention through the summer — my grandfather specifically, which is verifiable. That I intend to present myself properly rather than incompletely."
"That's very good," Mia said. "It tells him you're serious about commitment rather than casual. He'll respect that."
"It buys us the summer." She set the note down. "After the summer—"
"After the summer we'll have a different problem."
"Yes." She looked at Mia directly. "But after the summer we'll have five months of joint casting practice and hopefully three more Horcruxes."
"Hopefully," Mia agreed.
Bellatrix picked up her quill and started drafting.
Mia watched her write — the careful, considered precision of someone composing a lie that had to be as close to the truth as possible to hold up, which was its own kind of dark art and Bellatrix was brilliant at it.
"Training tomorrow," Bellatrix said, without looking up. "Early."
"How early."
"Five thirty."
"Five thirty."
"We're adding the Legilimency component. It requires more time." She looked up briefly. "Your Occlumency surface has improved significantly. Three weeks ago I was in your mind in under ten seconds. This morning it took me four minutes."
"Four minutes isn't very long."
"Against anyone else it would be plenty." She looked back at her draft. "Against Voldemort we need it to hold indefinitely. We're not there yet."
"We'll get there."
"We'll get there," she agreed, and went back to writing.
Mia looked at the note from Voldemort sitting on the desk. At the mark pressed into the wax. At the careful distance between where they were and where they needed to be.
Then she looked at Bellatrix — dark head bent over parchment, quill moving, the firelight warm on her face, entirely focused and entirely herself.
We'll get there, she thought.
She believed it completely.
The last training session before the N.E.W.T.s started was a longer one.
All three of them — Mia, Bellatrix, Avery — in the fourth floor classroom at six in the morning with the windows grey and the floor cleared and the particular serious energy of people preparing for something they couldn't entirely see yet.
Avery had been training with them for three weeks. He was good — technically precise, strong defensive instincts, better under pressure than his common room composure suggested. Bellatrix had taken his ward dismantling apart and rebuilt it twice and he'd come back each time better, which was apparently the only qualification she required.
"The joint casting sequence," Bellatrix said. "From the beginning. Avery, watch the handoff points — that's what you're learning today."
"I'm not going to be part of the soul reversal casting," he said.
"No. But you need to understand the mechanism so you can protect it." She looked at him. "When we do the final stage there will be a window of vulnerability. Both of us will be entirely focused on the casting. Someone needs to be watching the room."
He nodded. "So I need to understand what I'm watching for."
"Exactly." She turned to Mia. "Ready?"
"Ready."
They went through the joint casting sequence — the lead and follow rhythm, the magic running between them in the pattern they'd been building for months. It was different now from Little Hangleton, different even from the locket. More instinctive. The handoffs happened without signal, the magic finding its own path between them.
Avery watched with the focused attention of someone learning by observation, which he was very good at.
When they finished he said, "The handoff at stage four. That's the vulnerability window."
"Yes," Bellatrix said. "The lead switches. There's approximately one second where neither of us is fully in control of the combined cast."
"One second where someone could interrupt."
"One second."
He thought about it. "I can cover that. What am I covering against?"
"Anything," Mia said. "In the final confrontation there will be Death Eaters. There will be Voldemort. There will be chaos." She paused. "You're not fighting them. You're buying us one uninterrupted second."
"I can buy you one second," he said. "Probably more."
"More would be better," Bellatrix said.
"More is what you'll get." He rolled his shoulder. "Again. I want to see the stage four handoff three more times."
Bellatrix looked at him with the expression she got when something met her standard.
"Again," she said to Mia.
They went again.
Outside the window the sky was moving from grey to pale gold and the castle was beginning to wake around them, and in the fourth floor classroom three people who were going to need to be ready practiced being ready, and the morning opened up around them like something that had been waiting to.