He asked to stay after on the Tuesday of the first week of December.
The session had run its two hours, covering the specific application of sustained-output theory to mobile combat — the question of how to maintain a high-demand working while moving, which was the technical challenge that most defensive magic glossed over because most defensive magic was designed for static positions, and real conflict was not static. Dumbledore had been, as he always was in these sessions, fully present and precise in a way that communicated the respect of one serious practitioner for another, which was one of the things about the Tuesday sessions that Ron had not anticipated and had come to value in the specific way of things you did not know you needed until you had them.
After the session, Dumbledore settled into his chair with the quality of someone allowing themselves the rest that two hours of high-concentration teaching required. Ron stood.
'I need to tell you something,' he said. 'About what's coming in December.'
Dumbledore looked at him. 'Sit down,' he said.
He sat.
'Voldemort's snake,' he said. 'Nagini. She's his last remaining Horcrux — the mobile one, the one he keeps with him. He uses her as an instrument for actions he doesn't want traced directly to him.' He paused. 'She's going to be sent to the Department of Mysteries before Christmas. I don't know the exact night — the specific trigger in the original timeline has been disrupted by changes we've already made — but the strategic logic that produced the attack is still in place. He wants access to the Department. She's how he gets it.'
Dumbledore was very still. 'You're certain of the timeline.'
'Certain enough to act on,' Ron said. 'Before Christmas. Possibly before the twentieth. I'd recommend continuous Order presence at the Department from the fifteenth onward, rotating so no one is there long enough to be fatigued.'
'And Nagini,' Dumbledore said. He said the name with the specific quality of someone who was hearing it in a new register — not the snake, not the weapon, but the Horcrux, the container of a soul fragment. 'She cannot be killed with a standard curse.'
'No,' Ron said. 'She needs to be destroyed in the way a Horcrux requires — something that damages at the fundamental level. Basilisk venom is available in quantity. The Sword of Gryffindor is available. Fiendfyre would work but is too dangerous to use in a confined space.' He looked at Dumbledore. 'Whoever is on guard needs to have the Sword or any goblin steel imbued with venom and needs to know that a normal killing curse might not be sufficient. They don't need to understand why. They need to trust the instruction.'
Dumbledore absorbed this. 'Who do you suggest?'
'Tonks or Shaklebolt,' Ron said. 'They are both capable, reliable, and has the specific quality of someone who will follow a careful instruction on faith when the source of the instruction has earned that faith. They have my direct respect if that helps the decision.'
Dumbledore looked at him with the expression he reserved for moments when the conversation had moved somewhere he had not expected. 'It helps,' he said, after a moment. 'I'll arrange it with them.'
'And they should be told, after, what it is done,' Ron said. 'Not the full picture. But enough to know it mattered. Killing something that is partly a Horcrux produces a specific feeling — wrong, not like a normal animal death. They'll have questions. They deserves the beginning of an answer.'
'Yes,' Dumbledore said. 'I'll see to it.'
He stood to go.
'Mr. Weasley,' Dumbledore said.
He stopped.
'This is the last of the Horcruxes outside Voldemort himself and the cup in our possession,' Dumbledore said. 'After this, the structural anchors are gone. What remains is the final confrontation.' He paused. 'Are you ready for that conversation? Not tonight — in the new year, when we have the clarity the death of the last Horcrux will provide.'
'I've been ready for that conversation since second year,' Ron said. 'I've just been waiting for the conditions to be right.'
'Then we will have it,' Dumbledore said, 'in the New Year.'
He learned about it on the seventeenth.
He was in the library after dinner — the east window table, the dark-covered notebook open to the ward theory work, the December dark outside the glass — when Dumbledore appeared in the doorway with the quality of someone carrying news and having come to deliver it in person rather than by owl.
He looked up. Something in Dumbledore's expression told him before the words did.
'It's done,' Dumbledore said.
He put his quill down.
Dumbledore crossed to the table and sat down across from him in the way he sat in the Tuesday sessions — fully present, the occasion requiring presence rather than distance.
'Tonks was on duty from midnight,' Dumbledore said. 'Nagini came through the east corridor, which is consistent with your assessment of the approach Voldemort would have selected. She had the Sword and she understood the instruction. She did not hesitate.' He paused. 'She is physically unharmed. She is —' he chose the word carefully — 'affected.'
'The soul fragment,' Ron said.
'Yes. She described it to me as killing something that felt wrong in a way she couldn't name. Wrong in the way that things with something unnatural in them feel wrong when they die.' Dumbledore looked at him. 'She is asking questions I have promised to begin answering.'
Ron looked at the window. Outside, the December sky had the specific quality of Scotland in mid-winter — not quite snow, the air holding the possibility of it. He thought about Tonks in the corridor of the Department of Mysteries with the Sword in her hand, doing a thing she had been asked to do on faith, and the feeling it had left her with, and the faith it had required, and the fact that she had not hesitated.
'She should know she's a hero,' he said. 'Without the full context, she won't understand why. But she should know.'
'I told her,' Dumbledore said, 'that what she destroyed tonight has shortened this war in ways she may never be able to fully understand, and that I am grateful, and that what she felt was real and not a weakness.' He paused. 'She said: I know it's not a weakness. I just want to understand what it was.'
'Good,' Ron said. 'That's the right question.'
He sat for a moment with the specific quality of having received what he had been working toward since June and having it be exactly what it was supposed to be — not triumphant, not relieved in the showy sense, but the specific settled feeling of a step completed and the work continuing.
Most of the Horcruxes were gone. The Cup retrieved to be destroyed as a distraction. The ring which Dumbledore and Snape and Moody had retrieved from the Gaunt shack in October and destroyed. Nagini, destroyed tonight in a corridor in the Ministry. The diary, the locket, the diadem — in the Chamber, in the Room of Requirements, years ago now.
Voldemort himself remained. But the anchors were almost gone, and what that meant was a different conversation, for January, when the shape of the final year was clear.
'What does Snape's intelligence say?' Ron asked.
Dumbledore's expression settled. 'He will contact me tomorrow morning,' he said. 'I will tell you what the report contains.'
The report came the following afternoon, passed to Ron in a folded note delivered by Fawkes to the library window — Dumbledore's handwriting, three sentences, which was the entirety of what the session with Snape had produced that was relevant:
Voldemort's reaction was significant. The inner circle is frightened — not of him specifically, but of the quality of the rage, which has no direction because the means of Nagini's death is not known. Snape's assessment: the Azkaban breakout will be accelerated. Timeline has moved forward.
He read it twice. He folded the note and put it in the dark-covered notebook.
He adjusted his calendar.