The first day back after Christmas, Sirius Black cornered Mia in the corridor outside Potions.
Not threateningly — Sirius didn't really do threatening, he did relentlessly present — he just appeared at her side between one step and the next with the energy of a large dog who had been inside for a week.
"You survived Christmas at Grimmauld," he said.
"I did."
"With my mother."
"She tested my genealogical knowledge back to 1612. I passed."
He stared at her. "Nobody passes that."
"I studied."
"Nobody studies for that. It's not a thing people study for." He fell into step beside her, hands in his pockets, looking at her sideways. "My mother told my father you were acceptable."
"High praise."
"From her it's basically a standing ovation." He paused. "She also said you had backbone. That's the best thing she says about anyone. She said it about Churchill once."
"I'm honoured to be in that company."
"You should be, he's the only Muggle she's ever respected and I'm fairly sure she doesn't know he's a Muggle." He grinned. "Also Bella was almost a human person at Christmas. My cousin Andromeda wrote to me about it. She said Bella laughed at dinner."
"People laugh at dinner."
"Bella doesn't." He looked at her with those sharp grey eyes that missed considerably less than his general chaos suggested. "You're good for her."
Mia looked at him. He was fifteen and already more perceptive than he'd ever get credit for, and she thought about everything she knew about how his life turned out and felt the familiar ache of it.
"She's good for me too," she said honestly.
Sirius seemed satisfied with this. "Right," he said. "Good." Then, seamlessly, as if the conversation had always been heading here: "Also can you help me with my Transfiguration essay because McGonagall hates me and I need someone whose notes she won't immediately recognise."
"Absolutely not," Mia said.
"I'll owe you a favour."
"Your favours seem chaotic."
"They're extremely useful if you need something broken into."
Mia paused for just a fraction of a second. "I'll think about it," she said.
---
She told Bellatrix that evening.
They were in Bellatrix's room, the Horcrux list spread between them on the desk, two cups of tea going cold at the edges. Bellatrix had been annotating in red ink for the past hour, cross-referencing everything Mia knew against her own knowledge of Dark object provenance, and she had the focused slightly-terrifying energy she got when a problem was becoming solvable.
"Sirius offered to break into something," Mia said.
Bellatrix didn't look up. "What did you say."
"I said I'd think about it."
Now she looked up. "You want to use my fifteen year old cousin as a burglar."
"He offered."
"He offers everything. He offered to duel Lucius Malfoy last year for a chocolate frog."
"Did he win."
"That's not the point." But the corner of her mouth moved. "What would we even need him for."
"Nothing yet." Mia looked at the list. "But the ring is in Little Hangleton. The Gaunt house. We can't exactly walk in during a Hogsmeade weekend."
"We can't exactly walk in at all. The Gaunt family magic is old and unstable. The house has been abandoned for decades — the wards will have degraded but unpredictably." Bellatrix tapped the list. "We need information before we go anywhere near it."
"Which means the restricted section."
"Which means the restricted section," Bellatrix agreed. She picked up her tea, found it cold, set it back down with a look of mild betrayal. "And possibly the Black family library. There's documentation on the Gaunt line going back several generations. My grandfather's collection."
"The archive."
"Different section. Genealogical records, not correspondence." She paused. "Actually accessible."
"So we have a plan."
"We have the beginning of a plan." Bellatrix leaned back in her chair and looked at her. The red ink was on her fingers. Her hair was slightly dishevelled from hours of work and she was wearing an old Hogwarts jumper she'd clearly had for years, nothing like the composed person she was in corridors and common rooms, just herself.
Mia thought, not for the first time, that this version of her was her favourite.
"What," Bellatrix said.
"Nothing."
"You have a face."
"I have a neutral expression."
"You have never had a neutral expression in your life." She studied her. "You're doing the thing where you're thinking something you've decided not to say."
"I'm thinking that you have red ink on your nose."
Bellatrix's hand went to her face immediately and Mia laughed and Bellatrix looked at her with profound indignation.
"There's no ink on my nose."
"There really isn't," Mia agreed, still laughing. "I'm sorry. Your face—"
"Was perfectly reasonable given—" She stopped. Pointed her red inked finger. "You're going to pay for that."
"I'm terrified."
"You should be." But she was almost smiling now, the indignation losing the battle with the corner of her mouth. She stood up and crossed the room and Mia tipped her chin up and Bellatrix kissed her with great deliberateness, which effectively ended the laughing.
When they separated Bellatrix looked at her very seriously. "Restricted section. Tomorrow night."
"Tomorrow night," Mia agreed.
"And you're helping me re-annotate section three of the list."
"Also fine."
"Good." She went back to her chair and picked up her quill and the composed focused person was back, except for the ink on her fingers and the fact that she was visibly trying not to smile.
Mia picked up her own quill and got back to work.
—
The restricted section at midnight was familiar territory by now.
They had a system — Bellatrix dismantled the ward on the gate, Mia managed the Silencing charm on the floor because Bellatrix's version was technically superior but Mia's was quieter and the difference mattered at midnight. They moved through the shelves without lighting their wands until they were deep enough in that the light wouldn't reach the windows.
"Dark object provenance, Gaunt family," Bellatrix said quietly, already scanning the shelves. "It'll be cross-referenced under Slytherin descendants. And possibly under cursed objects, if whoever catalogued this had any sense."
"Who catalogued the restricted section."
"Pince, presumably, and someone before her." She pulled a volume, checked the index, replaced it. "There was a librarian in the 1800s who organised the entire section by perceived moral danger. Everything about the Gaunts would be at the extreme end."
"How do you know that."
"I have spent," Bellatrix said, pulling another volume, "a genuinely unreasonable amount of time in this section." She found what she was looking for and brought it to the reading table. "Here."
The Gaunt family entry was extensive and not encouraging.
"Inbreeding," Mia said, reading. "Extensive."
"The Gaunts were obsessive about bloodline purity even by the standards of people who were obsessive about bloodline purity." Bellatrix turned a page. "By the time Tom Riddle's mother was born the family was down to three people and none of them were entirely stable."
"Merope managed to produce Voldemort."
"Merope managed to produce Voldemort," Bellatrix agreed, in the particular tone of someone acknowledging a fact they find complicated. "The house is in Little Hangleton. Has been in the family since the 1600s." She turned another page. "Wards — here. Blood wards, primarily. Active as long as a Gaunt with magic is living." She looked up. "The last Gaunt died in Azkaban in 1943."
"So the blood wards are dead."
"The blood wards are dead. The residual magic isn't." She read further. "There are passive curses on the property — standard pureblood protection, decay charms rather than active hexes. The kind that accrue when a magical house is abandoned." She closed the volume and looked at Mia. "It's manageable. The ring itself is the problem."
"The ring has a curse on it." Mia kept her voice even. "A bad one. In my timeline Dumbledore put it on without thinking and it nearly killed him."
Bellatrix stared at her. "*Dumbledore* nearly killed himself with it."
"He was also trying to use it for personal reasons which—" She paused. "Long story. The point is the ring has a curse independent of its being a Horcrux. We go nowhere near it without full curse-breaking preparation."
"I can break most curses."
"Not this one on its own. We need to research it first." She held Bellatrix's gaze. "I mean it. This one we do properly."
Bellatrix looked at her for a moment. "You've seen what it does."
"I've seen what it did to the most powerful wizard of the century," Mia said. "So yes. Properly."
"Properly," Bellatrix agreed, without argument, which meant she'd heard the seriousness in it. She turned back to the volume and began copying the ward information in her neat red-ink hand. "We'll need three weeks of preparation minimum. The right counter-curses, a containment vessel, a way to destroy it once it's contained."
"Fiendfyre can destroy a Horcrux. It can also destroy everything else in a twenty foot radius."
"So controlled Fiendfyre." She said it the way people say so we'll need milk when writing a shopping list.
"Can you cast controlled Fiendfyre."
Bellatrix looked at her with an expression that said the question was slightly beneath her.
"Right," Mia said. "Stupid question."
"A little." She finished her notes and rolled the parchment. "Three weeks. Then Little Hangleton."
"Then Little Hangleton," Mia confirmed.
Bellatrix stood and stretched and then stopped, looking at the shelf above the one they'd been using. Something had caught her eye. She reached up and pulled a thin, dark volume with no title on the spine.
"What is it," Mia said.
Bellatrix was already reading. Her expression shifted into the one it got when something had genuinely surprised her. "It's a theoretical framework for soul division," she said. "Written in 1703. This predates most of the documented Horcrux theory by about a century." She turned a page. "This is — Mia, this has counter-theory. Someone was working on reversal methodology."
Mia went still. "Reversal of—"
"Of the soul division. Theoretically." She looked up. "It's incomplete. But it's here."
They looked at each other across the reading table in the dark library, both understanding at exactly the same moment what that could mean.
"Take it," Mia said.
Bellatrix was already putting it inside her robes. "Obviously," she said.
---
They were almost back to the gate when the noise happened.
Not a person — something on a shelf, one of the self-rearranging volumes losing its grip and hitting the floor with a sound that in a silent library at midnight was approximately the volume of a small explosion.
They both froze.
Footsteps. Distant but approaching. The specific unhurried pace of someone doing rounds.
Bellatrix grabbed her wrist and pulled her sideways into the gap between two of the taller shelves — barely wide enough, pressed together in the dark, Mia's back against old leather spines and Bellatrix a breath away facing her, both of them not moving.
The footsteps came closer. A light swept the end of their row. Pince's cat — the horrible one — appeared at the end of the shelf and stared at them with the morally superior expression of a creature who knew exactly what was happening and was deciding whether to care.
Mia stared back at it.
The cat held eye contact for what felt like an extremely long time. Then it turned and walked away with great dignity.
The footsteps paused. Then moved away.
They stayed still for another thirty seconds.
Then Bellatrix exhaled slowly against her cheek and Mia became very aware of how close they were in the dark, Bellatrix's hand still at her wrist, both of them breathing.
"The cat," Mia said quietly.
"Pince's cat is the only thing in this castle I find genuinely unpredictable," Bellatrix said, her voice low against her ear. "And I've accounted for most things."
"We should go."
"Yes."
Neither of them moved for another moment.
Then Bellatrix pulled back and smoothed her robes and was composed again, which was impressive given the circumstances, and they slipped out of the restricted section and up to the seventh floor without incident.
-—
Outside Bellatrix's door Mia leaned against the wall and looked at her.
"Three weeks," she said.
"Three weeks," Bellatrix confirmed. "Research first. Then the ring."
"And the book?"
"I'll have it translated and annotated by Thursday." Said as a simple fact. Bellatrix's relationship with reading speed was genuinely unfair.
"Of course you will." Mia paused. "This is going to work."
Bellatrix looked at her. The corridor was quiet and the castle was dark and she had that expression again — the private one, the one that only existed in empty rooms.
"I know," she said.
"I mean all of it. The whole plan. We're actually going to—"
"I know, Mia."
"I just want to say it out loud sometimes."
Bellatrix stepped forward and tucked a curl behind her ear and said, quietly, "I know. So do I." Her hand stayed at her jaw for a moment. "Get some sleep. You have Transfiguration at eight."
"You have Transfiguration at eight too."
"I don't need as much sleep."
"That's not how sleep works."
"It's how I work." She kissed her briefly. "Goodnight."
"Goodnight," Mia said, and meant a considerably larger thing by it, and from the look on Bellatrix's face as she closed the door she knew it.
She walked back to the dormitory in the dark and lay down without waking the other girls and stared at the ceiling with the feeling of something enormous and possible humming under her ribs.
A theoretical reversal of soul division.
Three weeks to the Gaunt house.
A list of seven objects that stood between them and the end of a war that hadn't started yet.
She fell asleep smiling.