A few hours later…
Well past midnight, the Headmaster's Office door gave a soft creak and swung inward.
Headmaster Jon stepped through, shoulders tired and coat dusted with the long night. Harry, a sixth-year from Gryffindor, trailed in behind him.
"All right, Harry," Jon said, turning back to him, voice gentle. "Thank you for the help tonight. You can head back to the Gryffindor common room. If you run into Mr Filch, tell him you're coming straight from me."
He paused. "And do your best not to tell anyone what happened this evening. Not even Miss Granger or Mr Weasley."
Harry nodded a little numbly. He clearly hadn't quite climbed out of the shock of what he'd seen.
"Then… good-bye, Jon," he said under his breath.
"Sleep well. Good night."
As the door closed behind Harry, the portrait-lined walls, which had been making a show of dozing with great dignity, sprang to life at once.
Voices rose in a flurry until the office sounded like a crowded market.
"How did it go?"
"What's it like in the Chamber? I want to see it!"
"Has the Defence Against the Dark Arts curse been broken?"
Questions overlapped, jostling for Jon's attention.
"Hold on," Jon said, shaking his head. "Could one of you fetch Professor Galatea Merrythought for me? I know it's late, and I'm sorry to wake her, but this is urgent."
"I'll go!" one of the former Heads volunteered.
"Good. Thank you, Everard."
Jon spoke while laying a parchment covered in cramped notes onto his desk. It held everything carved on the back of Slytherin's statue that he'd found in the Chamber; he'd copied it all, line for line.
"Those look like… Ancient Runes?" a portrait murmured.
"They should be," Jon said with a nod. "Magic Salazar Slytherin left behind. I suspect Tom used what's recorded here to lay the curse on the Defence post. I'll pass this to Professor Merrythought to see if she can find a way through."
"Is that all? Is that all?" Phineas Nigellus snapped, impatience crackling through his frame. "There must be more to the Chamber than that. Come on, out with it—when Dumbledore came back from the Chamber four years ago, he was just as maddeningly close-lipped as you are now—"
"There's really nothing else," Jon said with a helpless little shrug, wearing his most guileless expression.
He quite ignored the wall of sceptical looks aimed squarely at him.
Ten minutes later, Professor Galatea Merrythought arrived, bleary-eyed and wrapped in plaid pajamas.
"Headmaster Hart… at this hour…" she mumbled, still half in a dream.
"Forgive the disturbance, Professor," Jon said, all business now. "But the reason you gave before—how Tom Riddle managed to tap into Hogwarts' authority and lay a never-retire curse on you—I believe I've found it."
"Oh?" In an instant the years fell off her. Sleep fled. The problem involved her directly, and that had a way of sharpening anyone's attention.
Jon handed her the parchment dense with runes.
She took it, then unceremoniously sat right down on the floor and began to read, tracing the carved strokes with a forefinger.
"Such old magic… so precise," she murmured, almost to herself. "Hard to imagine it could be done this way…"
"Can you find a way to lift the curse?" Jon asked quietly.
"I think so," Merrythought said, sober and sure. "But it will take time. About a fortnight—at the very fastest."
"Good. I'll wait for your news," Jon said, exhaling, the tension in his shoulders easing.
"Don't worry, Headmaster. This old woman still has a trick or two."
When she had gone, Jon settled back into the high-backed chair. The portraits had tempered their hubbub and now sat with eyes closed, conserving their energy. At last, the room grew still enough for him to think.
Phineas had not been wrong. He had not told them the truth about the Chamber.
No more than Albus Dumbledore had, four years ago.
The basilisk below was not a "monster" in the way the world imagined. It was the guardian Salazar Slytherin left to Hogwarts. A thousand years earlier, the wizard had poured his thought and will—and his love for the school—into his serpent, setting that terrible creature to watch over Hogwarts in silence across the centuries.
Fifty years ago, Tom Riddle opened the Chamber. Unlike his ancestor, Tom had never known what love was. To him the basilisk was a tool, something to turn upon Muggle-born witches and wizards.
A natural Parselmouth could exert a crushing command over serpents. The basilisk remembered Slytherin's charge, but it could not ignore orders given in Parseltongue. It struck again and again at Hogwarts students.
It did its utmost to avoid killing. Even so, in the end, a student died.
Four years ago, Ginny Weasley, under the pull of Tom Riddle's Horcrux, opened the Chamber once more.
This time Albus Dumbledore went down as well. He was no natural Parselmouth and could not command the basilisk; but as a scholar who had studied widely, he could manage simple Parseltongue, enough to converse with serpents.
Through that conversation, Dumbledore learned the truth.
So he did not kill the basilisk. He brought it to the deepest place in the Chamber, into the open mouth of Slytherin's statue, where the grievously wounded guardian could rest and heal, to resume its watch.
To prevent panic, he told no one. He altered Harry Potter's memory and let the world believe Harry had slain the monster.
Until a few hours ago, when Jon and Harry went back into the Chamber…