The flames in the office fireplace flickered constantly.
However, after Sherlock cancelled the spell on the Dementor he had summoned and removed the sack, that soul-penetrating chill swept through the entire room.
A bone-chilling cold radiated from the Dementor, and its face, hidden beneath its robes, immediately began feeding on the hope and happiness of Sherlock, who was standing close by.
This feeding instinct remained the same, even though it had been captured.
Sherlock was completely indifferent to this. Compared to the straw man in the Goblin headquarters, the despair spread by the Dementor seemed negligible.
He waved his wand, tightening the silver threads binding the Dementor once more.
It was clearly visible that the Dementor was in great pain; the effects of the Patronus Charm were the natural enemy of these monsters.
Although the Original Owner was not proficient in the Patronus Charm, during his research at Azkaban, he had specifically used non-corporeal Patronus Charms to conduct experiments on Dementors.
The food that Dementors liked most and needed most for survival was the positive emotions of humans.
They fed on positive human emotions, and afterwards, they had to receive the feedback of fear.
In other words, Dementors were not simply feeding on hope and happiness; after draining these emotions, the victim had to exhibit fear and despair for the Dementors to be satisfied.
The reason the Patronus Charm was the nemesis of Dementors was that those silver beams of light contained only the positive emotions of hope and happiness, and the summoned Patronus was a semi-corporeal creature condensed from positive emotions.
A Patronus possessed only positive emotions and could not generate despair, so the Dementor could not harm it and would instead be repelled by such intense positive emotions.
But that was only enough to repel them.
As the most evil creatures in the world, Dementors could not be destroyed.
Since the discovery of these monsters, there had never been a single recorded case of a Dementor dying.
Even the most powerful Patronus Charm could only repel them or weaken their power, but there was no way to truly destroy them.
Of course, these were conclusions drawn by previous generations, and Sherlock intended to test them himself today to see whether they were accurate.
He directed his Patronus towards the Dementor, and the silver raven flapped its wings and circled above it.
The Dementor clearly showed signs of agitation. It seemed to want to escape, but it was tightly bound in place by the silver threads and could not move a single step.
Under Sherlock's control, the raven Patronus finally landed on the Dementor's head.
The Dementor appeared to be in extreme pain, with grey mist constantly emerging from its body. Within minutes, it became extremely weak and collapsed to the ground.
But there were no further reactions after that; the Dementor lay limp on the floor, Sherlock's Patronus stood on its head, and the black mist gradually stopped emerging.
The Dementor's condition suggested that it had merely lost the vast majority of its power, but there was no sign that it had been killed.
Normal spells, even the Killing Curse, were ineffective against them, and physical attacks could not even touch these monsters; the only thing that could affect them was the Patronus Charm.
But the Patronus Charm could not kill them either, only weaken their power and repel them.
Having verified these facts, Sherlock finally understood the Ministry of Magic's predicament and why it had ultimately chosen to cooperate with these creatures.
Dementors, which primarily relied on human emotions for sustenance, were inevitably the mortal enemies of humanity.
But these creatures could not be killed, and ordinary means could not cause them any harm.
Magic such as the Patronus Charm belonged to the highest level of defensive magic, and very few Wizards could successfully summon a Patronus.
If large numbers of Dementors were causing chaos everywhere, Wizards simply would not have enough manpower to repel them.
Therefore, the best solution was to gather them together and provide sufficient "food" to appease them, preventing them from causing havoc in populated areas.
Building Azkaban into a Wizarding prison and sending guilty Wizards there as food for the Dementors was the only practical solution to this predicament.
Dementors obviously did not care what status they held in the eyes of Wizards.
As long as someone provided them with enough food, they would obey that person, showing neither loyalty nor gratitude.
Sherlock smacked his lips as he looked at the Dementor sprawled on the floor. At first, he had thought there might be a way to destroy these creatures completely, but now it seemed he had oversimplified things.
If the Patronus Charm truly possessed lethal power against Dementors, ancient Wizards would never have allowed them to survive until the present day and would have eradicated these anti-human creatures long ago.
After hiding the weakened Dementor in the cupboard and sealing it with threads of the Patronus Charm, Sherlock clapped his hands and headed to the Great Hall to help Professor Flitwick finish decorating it for Christmas.
He still had a use for this Dementor later, so he could not let it return just yet.
The next day, Christmas Day, Sherlock woke up early and found a small pile of gifts stacked at the head of his bed.
He stared at them for a while, recalling that last year he had received only about half as many. Now they formed quite a respectable pile.
Of course, Sherlock had also sent out plenty of gifts, unlike last year when he had only sent Dumbledore a Christmas card.
However, the Christmas greetings attached to the gifts had not been written by him.
A week earlier, while he was preparing the presents, Harry had happened to be in the office. When he saw Sherlock writing the recipients' names on card after card—including Mrs Weasley, Mr Weasley, Dumbledore, and Professor McGonagall—he had gone so pale that Sherlock thought something was wrong.
Harry had hesitantly offered to write the greeting cards on Sherlock's behalf.
At first, Sherlock naturally refused, but after Harry begged so desperately that he was almost in tears, Sherlock finally relented and allowed him to write the cards.
As Harry sat at Sherlock's desk writing them, he felt immensely relieved and quietly proud.
He felt like a hero, saving Mr Weasley and the others from what would otherwise have been a disastrous Christmas.
The first thing to do on Christmas morning was naturally to open the presents.
Professor McGonagall had sent him another knitted hat, though this one was entirely black.
Mrs Weasley had sent him a pair of woollen trousers, and Kingsley had sent him a scroll on ancient defensive magic that looked extremely valuable.
There was also a complete set of wand-care tools from Fleur in France, and a brand-new Quick-Quotes Quill from Hilke.
To be honest, Sherlock was rather surprised to receive a gift from Hilke. He had never imagined that someone with her personality would give Christmas presents.
The same went for Fleur. He had not expected that, after nearly half a year, the little girl in France would still remember him.
The real problem was that he had not prepared gifts for either of them.
That made Sherlock, who believed strongly in reciprocity, feel rather awkward, as though he were some sort of villain with no social graces.
But since Christmas had already arrived, there was no way to make up for the oversight now. He could only wait until next Christmas and repay them twice over.
After opening his presents, Sherlock went to the Great Hall for breakfast. He still needed to help Professor Flitwick hang the remaining ribbons that had not been put up the previous day.
During the morning, he did not return to his office but instead chatted with Professor McGonagall in the staff room about various teaching matters.
The Christmas atmosphere in the Castle this year was noticeably quieter than last year because so few students had remained at school. Including the Professors who lived at Hogwarts year-round, there were fewer than twenty people altogether.
The atmosphere at lunch was still lively, however. The joy of Christmas allowed Harry to forget about Sirius Black for a while. In addition, he had received a Christmas present that morning from an anonymous sender: a new racing broom, the Firebolt.
At the dining table, under Dumbledore's enthusiastic encouragement, Snape reluctantly pulled a Wizard cracker, and a large witch's hat popped out and landed squarely on his head.
He wore a thoroughly displeased expression before removing the hat and pushing it towards Dumbledore, who cheerfully placed it on his own head.
There was one person noticeably absent from the table that day: Lupin had not come.
Professor Sybill Trelawney noticed his absence, and Dumbledore covered for him by saying that he was ill again.
In reality, these days coincided with the full moon in mid-December, and Lupin had almost certainly taken the Wolfsbane Potion prepared by Snape and gone somewhere to undergo his transformation.
After the Christmas feast ended, Sherlock returned to his office to continue a series of magical experiments on the Dementor.
When night fell over Hogwarts and moonlight streamed through the windows, he stuffed the half-dead Dementor he had been experimenting on back into the cupboard, then took the locket from around his neck and examined it beneath the moonlight.
He discovered that it looked even newer than before.
The changes in the locket were almost imperceptible from day to day, but after so many days it was obvious that it had changed since it had first appeared around Sherlock's neck.
Although it was still dark gold overall, the rust-like patches on its surface had disappeared, as though it had been carefully restored.
That change was enough to confirm Dumbledore's conclusion.
The locket was slowly repairing itself. What would happen once it had completely restored itself remained unknown.
Sherlock hoped Dumbledore was right—that the day it could finally be opened would also be the day it could be removed from around his neck.
Judging by its current rate of self-repair, that day probably would not be long in coming.