He planned it across the first three weeks of December in the specific quiet spaces between everything else.
The cards first. Three hundred and nineteen of them — every student staying at Hogwarts over Christmas, which included the Hogwarts contingent and the significant portions of the Beauxbatons and Durmstrang delegations who had not returned home for the holiday. The Witness had always worked through inclusion rather than exclusion, and Christmas was not an occasion to change that.
The card design was simple: the Hogwarts crest on the front, gold on deep green, and inside a single line in clean print: *Wherever you are from, I hope you enjoy the festivities at Hogwarts. Merry Christmas. — The Witness.* The Witness mark on the back, as always.
He spent two evenings in the Room of Requirements writing them by hand, which was not strictly necessary but felt correct — the difference between a card that had been produced and a card that had been made. Three hundred and nineteen cards. His handwriting by the end of the second evening had the specific quality of someone who had been doing the same thing for a very long time and had arrived at a rhythm.
The suits of armour were the more technically demanding part. He had done it with a single song. Now he had to do it with three.
He had been working on the enchantment since November, in the hour after the training sessions when the Room was still available and his mind was at its most precise from the sustained focus of the previous six hours. The enchantment had three components, which had to be sequenced correctly: the activation trigger, keyed to three in the morning on Christmas Eve; the song sequence, which required each suit to hold its part independently while remaining in harmony with the others; and the reset, which would return every suit in the castle to its original state by half past three.
The song sequence had taken the longest. Not the magic — the selection. He had thought about it carefully and arrived at three songs that worked as a sequence rather than simply as three separate pieces.
He applied the enchantment to each suit in the castle across three nights in the second week of December, moving through the corridors under the Invisibility Cloak in the specific patient way of someone with a long list and a methodology. There were one hundred and forty-two suits of armour in Hogwarts. He checked each one off as he went.
On Christmas Eve he went to sleep at eleven and set no alarm, because the enchantment was either correct or it wasn't and sleeping through it would not change that.
He woke at three fifteen to the sound of one hundred and forty-two suits of armour singing God Rest Ye Merry Gentlemen.
He lay in bed for a moment and listened.
It was — correct. The harmony was the specific quality of something that had been enchanted rather than rehearsed, which meant it was technically perfect and had the slight uncanny quality of voices that had never been uncertain. The sound moved through the castle with the resonance of stone walls that had been carrying music for a thousand years and knew how to hold it. From the dormitory he could hear the corridors and the staircases and somewhere further the Great Hall, all of it in harmony, the old carol filling the castle from the ground floor to the towers.
Then it changed.
The transition happened between one verse and the next — God Rest Ye Merry Gentlemen completing its final chorus and then, without pause, one hundred and forty-two suits of armour beginning Last Christmas with the full commitment of enchanted objects that had no self-consciousness about the material.
In the dormitory, he heard Seamus say something unintelligible, then: 'Is that — is that a Muggle song?'
He heard Dean, who had grown up with the song, produce a sound that was not quite laughter and not quite disbelief and was both simultaneously.
He heard, from somewhere below, what he was fairly certain was Viktor Krum saying something in Bulgarian that had the quality of a question no one could answer.
The song continued with complete conviction for its full duration. Every suit. Every corridor. The specific earnest quality of enchanted objects performing something they had been given to perform and giving it everything.
Then, in the silence after the last note, the castle seemed to breathe.
And then Silent Night began.
The suits of armour, together, in the specific quiet of a different kind of harmony — not the structured precision of God Rest Ye Merry Gentlemen, not the cheerful absurdity of what had just happened, but something that was simply itself. The old carol moving through the stone corridors of a thousand-year-old castle on Christmas, falling through the cold air of every room that was still and lit and occupied by people far from home.
He lay in bed and listened to all of it.
By the time the last note resolved and the castle went quiet, Harry was sitting up in his bed across the dormitory with the expression of someone who had been woken by something unexpected and had arrived, by the end of it, somewhere he had not expected to arrive.
'That was you,' Harry said.
'The Witness,' Ron said.
Harry looked at him. 'Ron.
'Go back to sleep,' Ron said. 'The cards will be there in the morning.'
Harry lay back down. After a moment: 'Last Christmas?'
'It felt right,' Ron said.
A pause.
'It was right,' Harry said. He sounded, Ron thought, like someone who had received something they had not known to want. 'Goodnight, Ron.'
'Goodnight,' Ron said.
The castle was quiet. Outside the grounds were dark and cold and still under a December sky, and somewhere in the corridors three hundred and nineteen cards were waiting in their envelopes for morning.