Mole was reading correspondence when Rowan knocked on Friday morning. She waved him in without looking up, finished the letter she was on, set it aside, and folded her hands.

  "Mr. Ashcroft. I was going to summon you today if you hadn't come on your own. Sit down."

  He sat. The office looked the same as it had in first year. Portraits of former headmasters dozed in their frames along the walls. A brass telescope stood by the window. The desk was buried in parchment.

  "The Department of Magical Law Enforcement sent an investigator to your shop over the summer," Mole said. "An Officer Singer. Professor Weasley informed me of the details. I gather the investigation was not what you'd hoped."

  "She spent three hours in the shop, took some notes, and classified the case as inconclusive due to insufficient evidence. The attackers left nothing behind."

  "They left you behind," Mole said. "You were there. You saw their faces, heard their voices, watched them cast. That's evidence, Mr. Ashcroft, even if Officer Singer didn't think to ask for it in a form she could use."

  She stood and crossed to a cabinet behind her desk. Inside, on a shelf between a stack of old ledgers and a jar of something that moved, sat a shallow stone basin carved with runes around its rim. She carried it to the desk and set it between them.

  "This is the school Pensieve. I've used it twice in my tenure, both times to resolve disputes between students who couldn't agree on what happened. It allows the extraction and viewing of memories in their complete, unedited form." She looked at him. "I'm offering it to you now. Extract what you remember of the attack. Officer Singer may have closed her investigation, but a set of Pensieve memories delivered to her desk gives her something she can't ignore."

  Rowan looked at the basin. The runes around its rim were old, the carving style predating anything Fenwick had shown them. The surface of the stone was polished smooth from use. He'd read about Pensieves in Moonstone's advanced text, the theory of externalising memory through wand contact at the temple, but he'd never had access to one.

  She produced a set of small glass vials from a drawer. "These are for storage and transport. Seal them properly and they'll keep indefinitely."

  Rowan drew his wand. He thought about the attack. The anti-Apparation ward settling over the building. Clara's voice, barely a whisper, identifying what it was. The five figures crossing the square. The way they moved, weight centred, wand arms loose.

  He placed his wand to his temple and pulled.

  The sensation was cold and strange, like drawing a thread through the inside of his skull. A silver filament came with the wand tip, shimmering, and he lowered it into the first vial. Mole sealed it with a tap of her wand.

  He extracted three more. The first exchange of spells. The moment Athena struck the attacker's face. The word that dropped the ward and pulled every body from the room.

  The last one was harder. Clara on the floor. The Cruciatus. He had to hold the wand steady while his mind replayed the sound she'd made, and his hand shook, and the memory came out ragged at the edges.

  Mole sealed it without comment. She lined the four vials on her desk and looked at them for a moment.

  "I'll have these sent to Officer Singer by school owl this afternoon, along with a letter from me on Hogwarts letterhead requesting the case be reopened. The letter will note that a student under my care was subjected to an organised attack by multiple adult wizards using dark magic, and that the DMLE's initial investigation failed to collect available evidence." She met his eyes. "A Headmistress's letter carries weight. Even with the DMLE."

  "Thank you, Headmistress."

  "Don't thank me. You should have had this option weeks ago. The fact that nobody offered it is its own kind of failure." She began returning the Pensieve to its cabinet. "Is there anything else?"

  Rowan hesitated. The vault was on his mind but whatever was stopping him from telling Iris last night would stop him here too. He could feel it, the closed door in his throat, ready to slam shut if he tried.

  "No, Headmistress. Thank you."

  He left the office and descended the spiral staircase. The vials were on their way to Singer. Whether anything came of it was another question, but at least the evidence existed now, outside his head, in a form that couldn't be dismissed.

  The cursed vault had been on his mind all week.

  Peeves had said that Rowan had been walking past it for years. The fifth floor was where he went to Ancient Runes with Fenwick, where the Charms corridor connected to the main staircase, where he cut through on his way to the library three times a week.

  That night he pulled out the journal from first year, the one where he'd catalogued his Christmas explorations of the castle. Dungeon corridors and their contents. Tower staircases and secret passages. And one entry with a sketch of archaic runes surrounding a warded door deep beneath the castle that he'd never been able to open. He'd noted the feel of it, the sense of old magic pressing outward from behind stone. He remembered that sensation clearly. If the vault door felt anything like the dungeon door, he'd recognise it.

  On Friday afternoon, after Runes, he walked the fifth floor corridors differently.

  He went slowly. Past the Charms classrooms, past the portrait of the sleeping knight that snored so loudly you could hear it from the stairwell, past the alcove where a suit of armour stood guard over nothing in particular. He was paying attention to the walls, to the feel of the stone under his feet, to the ambient magic that lived in the fabric of the castle.

  At the far end of the corridor, past the last classroom, the passage turned left toward a staircase that students used to reach the sixth floor. Rowan had taken that staircase hundreds of times. He'd never stopped at the section of wall where the corridor turned, because there was nothing to stop for. A blank stretch of stone between a tapestry of trolls in tutus and a window that overlooked the courtyard.

  He stopped now.

  There it was. The same pressure he'd noted in his journal beside the sketch of the dungeon door. Old magic, locked and waiting, pressing outward from behind the stone. He'd been walking through it for two years without ever turning his head to look at it. Now that he was standing still and paying attention, he couldn't understand how he'd missed it.

  You could be reading stolen content. Head to Royal Road for the genuine story.

  He reached out and touched the wall.

  The stone burned when he touched it. A deep biting chill that had nothing to do with the temperature of the corridor. It seeped into his fingers and up his wrist and he pulled his hand back. His fingertips were white.

  He pressed his wand to the stone. A diagnostic charm returned nothing useful, just the dense magical signature of Hogwarts itself, layered so thick that any individual enchantment was lost in the noise. He tried a Revealing Charm. The wall shimmered but held.

  He pushed magic into the stone, steady pressure, the way you'd lean on a door to test whether it was locked. The wall resisted for a moment and then something shifted. The stone between the tapestry and the window folded inward, silently, revealing a narrow staircase that climbed steeply upward. The steps were covered in frost. The air that came out of the passage was bitter, far colder than it should have been, and Rowan's breath misted as it hit the threshold.

  He climbed. The frost thickened with every step, the walls narrowing until his shoulders nearly touched both sides. Ice had formed along the ceiling in crystalline ridges that caught the light from his wand and threw it back in fractured patterns. The temperature dropped with every step, pressing through his robes, and he cast a warming charm that lasted about thirty seconds before it guttered out.

  At the top of the stairs, a door. A wall of ice, floor to ceiling, blue-white and opaque, with a depth to it that suggested it went back further than the eye could reach. The surface was smooth except for a pattern etched into its centre, a shape that might have been a crest or a seal, the lines filled with something darker than the surrounding ice.

  Rowan touched it. It burned his skin on contact. He pulled back with a hiss and looked at his fingertips, which had gone from white to an angry red.

  He cast Incendio. The fire hit the ice door and vanished. No melting, no steam, and no hiss of contact. He poured more power into a second attempt, sustaining the flame, pushing heat against the surface until his wand arm ached with the effort. The fire washed over the ice and disappeared into it as though the door were drinking.

  Something moved behind the ice.

  Rowan stepped back. Through the blue-white surface, blurred and enormous, a shape was forming. It resolved slowly, like something rising from deep water. Armour. A helm. A sword that coalesced from the ice itself, edges forming as Rowan watched, sharp and deliberate.

  The Ice Knight stepped through the door.

  It was eight feet tall. The armour was ice, every piece of it, plate and chain and gauntlet rendered in a substance that looked like frozen steel but moved with the fluidity of something alive. The helm had no visor. Behind it, where a face should have been, there was only a blue-white glow that pulsed in slow rhythm, like breathing.

  It raised the sword.

  Rowan threw a Protego between them. The sword came down and the shield shattered on contact, the pieces dissolving into frost that hung in the air. The force knocked Rowan back a step and the cold from the impact ran up his wand arm into his shoulder.

  He fired a Confringo at the Knight's chest. The explosion detonated against the armour and the ice absorbed it. The blast, the heat, the concussive force, all of it drained into the Knight's body and the glow behind the helm pulsed brighter.

  It was feeding.

  Rowan threw everything he had. Stupefy, Flipendo, Diffindo, Bombarda. Every spell hit the Knight and every spell was absorbed. The glow grew brighter with each impact. The Knight took a step forward with each feeding, the frost on the ground spreading outward from its feet, and the cold intensified until Rowan's teeth were chattering and his wand hand shook.

  The sword came again. Rowan dodged left and his foot slipped on the frost and he went down on one knee. The blade passed close enough to his head that he felt the cold of it in his skull, a sharp, piercing ache behind his eyes.

  He rolled and cast Incendio from the floor, a sustained blast, desperate. The Knight walked through it. The fire wrapped around the armour and disappeared and the Knight didn't slow down.

  Rowan scrambled backward down the stairs. The Knight followed for three steps and then stopped. It stood at the top of the staircase, sword lowered, the glow behind its helm dimming slowly. It watched him retreat. Then it turned and stepped backward into the ice door and the surface closed over it and it was gone.

  Rowan sat on the stairs with his back against the frozen wall, breathing hard. His robes were stiff with frost. His wand hand was shaking from cold and spent adrenaline. The warming charm he cast this time lasted longer, away from the door, but the chill had settled into his bones.

  Peeves had been right. Everything he knew wasn't enough.

  He went to the library that evening and pulled every book on animated guardians, enchanted armour, ice magic, and defensive constructs. He read until the library closed and then continued in the common room, working through the stack while Iris studied across the table.

  She glanced at his reading material twice but didn't ask. She was still waiting for him to explain what had happened on Thursday, and the fact that she hadn't pushed was Iris being patient, which meant she was going to push eventually and it would be worse for the delay.

  Saturday morning. The stacks had given him nothing useful. The animated armour in the books responded to standard countercurses, which the Knight clearly didn't. The ice magic texts described enchantments that could be melted with sufficient heat, which he'd already tried. Nothing in the standard collection addressed a guardian that absorbed offensive magic and grew stronger from it.

  He went to the Restricted Section after breakfast, while the library was empty. His access from Hecat, granted second year for duelling research, still held. The rope barrier parted for him.

  The books here were still different. They didn't only sit on shelves. Some of them breathed. One growled when he reached for it. Another had a chain through its spine that rattled when he pulled it out.

  He found what he was looking for in a slim volume bound in dark leather, wedged between two larger books on cursed objects. The title was stamped in tarnished silver: Ignis Maledictus: A History of Cursed Fire.

  The book opened easily. The first chapter was a taxonomy of magical fires. Standard fire spells, Incendio and its variations, produced flame that behaved according to known physical and magical laws. It burned fuel, consumed oxygen, and could be extinguished.

  Cursed fire was different.

  The chapter described three kinds. Gubraithian fire, which burned eternally but was not destructive. Ashwinder fire, a byproduct of magical neglect. And Fiendfyre.

  Fiendfyre. Cursed flame of immense power, capable of destroying virtually anything, including objects enchanted to resist conventional magic. It burned through protective enchantments, consumed cursed objects, and could not be extinguished by any known counterspell. It took the form of monstrous creatures, serpents and chimera and dragons, and it had a will of its own that resisted the caster's control.

  The text was blunt about the danger. Of the twenty-three recorded attempts to cast Fiendfyre described in the volume, nine had resulted in the death of the caster. Four had caused destruction so widespread that entire buildings were consumed before the flames could be contained. The most recent recorded use was by a dark wizard in 1747 who had destroyed a Goblin-warded stronghold and himself in the process.

  Rowan read the passage three times. An ice guardian that absorbed every spell thrown at it. A fire that destroyed anything, including objects enchanted to resist conventional magic.

  He could see the logic. The vault was designed so that the only way through was a spell most wizards would never learn and couldn't control if they did. The cost of entry was the willingness to use magic that could kill you.

  He closed the book and put it back on the shelf.

  He wasn't going to learn Fiendfyre. The spell was classified as dark magic for a reason. Nine dead casters out of twenty-three attempts. A fire with its own will that resisted control. Even Grindelwald, who would one day master it, used it as a weapon of war, something you unleashed when you no longer cared what it consumed.

  Rowan left the Restricted Section and walked through the empty library and down the stairs and out into the morning. The grounds were grey under an overcast sky. Iris, Lawrence, Poppy, and Edmund were meeting him at the forest edge in an hour.