Snow, Signals, and the After-Hours Problem
December arrived like a polite dare. The lake went sheet-metal; the sky wore its best grey. Snow stacked itself in thesis statements along the ramparts. Hogwarts approved.
Ravenclaw's eagle asked, "What invention lets you look right through a wall?"
"A window," Corvus said, checking the locket with a thumb, the black coin a steady note against his sternum. The door opened with frost-bright good manners.
In the Hall, porridge steamed; owls sulked under snow; rumor wore mittens. Gryffindor still vibrated with post-match legend. Slytherin had recovered enough to be smug again. Corvus filed both under predictable weather.
> 64. Winter constraints: crowded stairs, wet boots, low light, high mischief. Solve for traffic + warmth + dignity.
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Quiet Nooks, Loud Discoveries
The library smelled gloriously of paper and the rule of law. Quiet Nooks glowed a discreet blue above select tables; Madam Pince prowled with priestly satisfaction. At the catalog, Hermione triangulated around an index like a general with maps. Harry listened, learning how research breathes; Ron wrestled a quill as if it owed him money.
Corvus drifted by the drawers and, to the air (not to them), said, "People catalog people where biography lives; alchemists sneak into history under famous friends."
Hermione's eyes flicked up. "Thank you," she said, which in her dialect meant already cross-referencing. He left them to it. Good systems make courage cheap.
---
Controlled Variables: Winter Session
Behind the fourth gargoyle, the hidden classroom warmed like a hand around a mug. Fred and George lounged, Daphne Greengrass leaned in the doorway composed as a queen in a quiet scandal.
"Agenda," Corvus chalked. "Winter variables. Two proposals."
He drew the first lattice: CV-011 — Night Lines. A hair-thin, low-light thread along main corridors from curfew to lights-out—visible at knee height, gentle as moonpath, guiding feet without shouting rule.
"No tripwire?" George asked.
"No shame," Corvus said. "Only path."
Daphne's mouth tipped. "Slytherin won't complain if elegance escorts us home."
"Second," Corvus said, sketching curves that taught water manners, "CV-012 — Warm Step. Heat-siphon gutters on main entries. Keep the center strip dry; leave puddles for those who require splashing. Ethical puddles only."
Fred saluted with a mitten. "You're turning the castle into a civilized coat."
"Someone should," Corvus said. "We trial at dusk. Five minutes. Nothing permanent until Pince and Pomfrey stop glaring."
> 65. Winter kit: Night Lines: opt-in look; Warm Step: rush-hour only; both self-sheathing at curfew.
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McGonagall's Corridor Weather
Between classes, McGonagall met him with that expression that means your mischief passed committee.
"Mr. Black. Deputy's note: continue. Within sense."
"Within sense is my favorite leash," Corvus said.
She handed over a slim parchment. "Prefects will carry your 'Night Lines' along their routes. I expect no lantern parades."
"Only sober moonlight," he promised.
"Good. And Mr. Black—tea is available if you feel the urge to be heroic. Paperwork, if that fails."
"Terror keeps me honest," he said.
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Peeves, Redirected by Scholarship
On the Charms landing, Peeves dangled upside-down over a stack of essays, brandishing a quill like a dagger.
"Peeves," Corvus said mildly, "the trophy room claims your curves have gone provincial."
"Provincial?" Peeves scandal-shrieked, and vanished mid-insult. Distant clattering suggested proof by demonstration.
> 66. Poltergeist management, winter: insult his geometry; point at brass.
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Snape's Lab Weather
Potions in December was stone and steam. Warming Draught on the board; Snape's voice like flint on silk.
"Precision," Snape said. "Unlike sweaters, you cannot simply wear more of it."
They brewed. Corvus shaved salamander scales to perfect translucence; Susan cooled their cauldron in tight circles, practical as mittens; at the next table, a Gryffindor over-stirred the pepperup—steam began to whistle in the key of bad decisions.
Corvus pinched a whisper of ventus over the lip—no heroics, just physics—and the whistle flattened into a sigh. Snape arrived, saw both the problem and the restraint, and dispensed judgment like winter sunlight.
"Adequate," he said to Corvus, which is Snape for thank you for not making me praise you. "Five points to Hufflepuff for not making this worse."
Susan grinned behind her ladle. Corvus wrote on his cuff: Warmth via grace; not brute heat. (People, too.)
---
Night Lines, Live
Dusk iced the windows violet. Prefects unspooled Night Lines from little chalk-capped tins: a pale, knee-high thread that woke when eyes dipped toward lost and slept when company was good. Warm Step taught water to prefer the edges; the main strip dried without fanfare. Children stopped sliding into anecdotes.
Madam Pince's scowl softened by a molecule as she crossed a dry threshold. Madam Pomfrey, making rounds like winter's lawyer, stepped onto a Warm Step and didn't slip; her mouth did not exactly smile. This counted.
Daphne ghosted past as the corridors dimmed. "Your moonpaths flatter everyone," she said. "Even Slytherins."
"Architecture owes compliments," Corvus said. "It keeps tempers like mirrors keep dust."
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The After-Hours Problem
By ten, the castle wore hush like a cathedral. Night Lines glowed their thin invitation; Warm Steps cooled to virtue. Corvus walked a last loop because systems prefer to be thanked.
At the second landing, the coin against his sternum went cold. Not hostile—hollow. The kind of temperature a room gets when a person disappears from it without leaving.
He knew that weather now: absence masquerading as cleverness.
A corridor to his left rippled with almost-sound—air refusing to touch cloth. He did not follow. He spoke to the wall.
"Hallway," he said gently, "we have small feet abroad who think hiding is the same as safety. Please guide the others around them without fuss."
The Night Line brightened by a heartbeat, then thinned, carving a lane that curved naturally away. Footsteps drifted past the unseen gap; no collision; no shout; no prefect summoned. Witnesses or walls—not thresholds.
He whispered to the wood, "Good stairs," and the rail hummed smugly.
> 67. After-hours doctrine: treat invisibility like weather; protect traffic, not secrets. Do not engage the cloak. Choose wall.
At a turn, Hermione strode past with a jaw set for war and quill ink on her thumb, not invisible, not subtle, entirely correct. She did not see him. He let that be. The castle's wrong harmony—the one that had haunted the third floor—watched, bored for once.
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Tower, Frost, and a Nearer Ask
Ravenclaw's knocker demanded, "What can travel around the world while staying in a corner?"
"A stamp," Corvus said. "Also, rumor." The door chuckled bronze.
He set coin and locket on the sill; Paradox muttered judgment in her sleep. Frost wrote with tidy patience:
Good.
Then, as if reluctant to break its own rule, added: Nearer soon.
"Soon is not tonight," Corvus told the glass. "Tonight we built moonpaths."
Mystery Log:
> 68. Winter deliverables:
– CV-011 Night Lines live; traffic smoother; small panic ↓.
– CV-012 Warm Step live at rush; slips → zero; puddles preserved for moral education.
– Potions: warmth via elegance.
– After-hours: cloak detected; wall chosen; lanes adjusted.
68a. Doctrine refresh: Institutions by ritual; people by permission; stone by praise; secrets by absence management, not chase.
He doused the lamp. The castle, pleased to be treated like a partner instead of a puzzle box, purred itself toward sleep. Somewhere two floors below, a boy under a cloak learned the difference between hiding and being safe; somewhere farther, a mirror practiced its hunger on empty air.
Corvus lay back, palms behind his head, and let the Night Lines draw thin silver maps under his eyelids.
Night wore the corridors like a velvet rule. Night Lines glowed their thin, knee-high moonpaths; Warm Step cooled to manners. The coin at Corvus's sternum stayed cool—not warning, exactly. Absence.
He took the hint and went to the hidden classroom behind the fourth gargoyle. The room greeted him like a cupped hand. He chalked the heading:
> CV-013 — Invisibility Clause
Protect traffic, not secrets.
"Design brief," he told the air. "We don't uncloak anyone. We don't find anyone. We simply keep the corridor from colliding with a person who thinks they're a ghost."
He sketched a lattice that listened for displacement—pressure changes, robe-drafts, scuffless footfall—not faces, not names. When the net sensed a moving absence, it nudged Night Lines to drift half a step aside and taught doors to check their swing. Armor paused mid-salute. Suits of mail swallowed their squeak.
Ethical constraints:
– no logging, no trail, no memory
– fifteen-second decay
– opt-out for staff (some monsters are friendly)
He breathed power into the shape. It settled with the relieved sigh of a policy that should have always existed.
> 69. CV-013 (live, trial): shields collisions; touches nothing else; dissolves like a good rumor.
---
Field Test (Unscientific, Effective)
"Proof," said Daphne Greengrass from the doorway, hands in pockets, voice dry as a winter apple. She'd followed the smell of a new rule.
"I require an invisible volunteer," Corvus said.
Fred and George arrived like punctuation. "We brought Near-Enough Cloaks," Fred said (bedsheets, charmed to sulk).
"And a tragic commitment to science," George added.
Daphne draped herself in a sheet with the poise of a queen trying on peasantry. She walked the corridor. The Night Line curved a breath aside; a door paused, thought better, and opened in. Fred—also ghosted—tried to shoulder past; the line made a polite lane. No jostle. No reveal.
"Acceptable," Daphne judged, shedding the sheet as if it bored her. "Slytherin approves being escorted without being exposed."
"Ravenclaw approves preventing anecdotes," Corvus said, writing it down.
---
Filch, Rerouted; Peeves, Weaponized
At the second landing, Mrs. Norris became a question mark with fur. Filch followed with a lantern that wanted crimes.
"After hours, mm?" Filch rasped at the air, which smelled guilty on principle.
"Peeves," Corvus said pleasantly, "the trophy room called you derivative."
Peeves detonated from a lampshade with an operatic HA! and tore off toward brass and grievance. Filch swore in a way the stones forgave and charged after, Mrs. Norris corkscrewing like punctuation.
The Invisibility Clause bowed to the unseen child swaying against the wall and let him pass unbumped. No names. No chase. Witnesses or walls, not thresholds.
> 70. Cloak event (observed): traffic curved; Filch diverted; injuries 0; secrets kept; headache avoided.
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Staff Weather: Two Conversations, One Rule
McGonagall intercepted him as if the corridor had arranged it. "Mr. Black. I have noticed lanes curving at inopportune times."
"Only to avoid collisions," Corvus said. "We do not keep names. We keep children from becoming anecdotes."
A long, measuring beat. "Good," she said. "Do not make a list."
"I like systems, not dossiers," he said.
"See that you keep liking them," she replied, which counted as benediction.
Later, Snape materialized from a seam in the dark. "Black."
"Professor."
"If you continue to engineer away the school's most creative injuries, Gryffindors will invent louder ones."
"I am counting on their ingenuity," Corvus said.
A pause that might have been humor if starved. "Imagine more slowly," Snape added, almost gentle. He moved on, shadow in tow.
> 71. Staff notes: McG—approve/no ledger; Snape—sarcasm ≈ consent.
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The After-Hours Problem, Solved by Not Solving
Near midnight, the coin went slightly colder, like fog on the inside of glass. Down a side corridor: footsteps smoothed by too much caution; a whisper of cloak. The Clause nudged the Night Line aside and taught a latch to close softly. Two prefects drifted past, none the wiser, dignity intact.
Corvus stood with his palm on stone and let the castle hum under it. "We're partners," he said. The wall warmed a degree.
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Library Addendum: Amnesty Works
Back in the library, the Quill Amnesty box ticked eleven and tsk-tsk'd with grandmotherly competence. Quills slunk home from pockets like repentant cats. Madam Pince pretended not to preen. Hermione—hair tied back in an argument with gravity—did not look up from a biography of Nicolas Flamel, but her good hand flicked a silent thanks.
> 72. Amnesty uptake: high; theft ↓; civility ↑; Pince scowl elasticity ↑ (measurable).
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Tower, Frost, and the Near Ask
Ravenclaw's bronze eagle asked, "What can fill a room yet takes up no space?"
"Light," Corvus said, and stepped into it.
On the sill: coin and locket, twin moons of different weather. He did not open the locket. Promises are load-bearing.
Frost wrote with tidy patience:
Walls chosen well.
Then, under it, fainter: Nearer soon.
"I hear you," he told the glass. "Not tonight."
Mystery Log:
> 73. Deliverables:
– CV-013 Invisibility Clause live: curves paths, hushes hinges; no tracking; fifteen-second decay.
– Filch/Peeves redirected; casualties: pride (brass), none (children).
– Staff alignment: McG ✓ (no lists), Snape ≈ weather.
– Amnesty box: eleven-o'clock penitent parade continues.
73a. Doctrine (winter): Institutions by ritual; people by permission; stone by praise; secrets by absence management.
73b. Ask nearer—with witnesses.
Paradox muttered judgment in her sleep. The lake turned the moon over in its palm. Somewhere, a boy under a cloak learned that safety is a system, not a stunt. Somewhere else, a mirror practiced patience because someone had told it to.
"Steady," Corvus said to the tower.
The coin warmed—a small, sufficient yes—and Hogwarts, pleased that its boy kept choosing walls over thresholds, slept with good manners and excellent bones.