The Hall of Memories
There was only theory, and of course, there was no way to be certain whether this magic would ultimately work as Sherlock intended.
But he also had no way to find anyone to experiment with it.
He could only be certain that if the information in the Hall of Souls was correct, then it could succeed.
Whether it would work or not, Sherlock didn't dwell on it too much; he had done everything he could. As for whether it would succeed as he predicted, that would depend on fate and Snape himself.
Coming out of the Hall of Souls that day, he tidied himself up, ate a full meal, left Amy at the Department of Mysteries, and returned to the Leaky Cauldron.
After Sherlock went to the Ministry of Magic, Snape had remained there.
He had no attachments in this world other than Lily, and besides trying to find a way to save Lily, he didn't know what else he could do.
When Sherlock pushed open the door and entered, Snape was in the middle of tossing a rat's liver into a cauldron. He looked up, staring at Sherlock with a blank expression.
"What are you back for?"
Sherlock stretched, collapsing into a chair as soon as he entered.
"What? Not happy to see me? If you don't want me here, I can leave, but don't expect to get the method to save Lily either!"
He said this, but his body showed no sign of moving; he remained sprawled lazily in the chair.
Having spent these past few days working tirelessly through those obscure and difficult materials, Sherlock had lost three pounds. Now that he was relaxing, he was too lazy to make any unnecessary movements.
Upon hearing Sherlock's words, Snape froze as if hit by a Petrificus Totalus, standing there completely motionless.
The Potion boiling in front of him continued to bubble, as if urging him to add more ingredients, but Snape had no heart to care about the Potion now; his eyes were fixed intently on Sherlock.
"You... you're telling the truth!"
"Don't get so excited yet. Listen to me finish first," Sherlock advised him.
But clearly, his advice had no effect. Snape was unable to calm down at all; the usual indifference on his face had vanished without a trace, replaced by extreme agitation and urgency.
"Speak, I'm listening." He took a deep breath, struggling to suppress the uncontrollable emotions in his heart, and sat in another chair to listen to Sherlock.
"I told you before that I had some leads regarding Lily. That's because I found the source of the soul magic she used to protect Harry," Sherlock said in a low voice.
"It is an unquestionable part of history that Lily used this magic on Harry in the end. Harry's scar, the Dark Lord's Killing Curse rebounding to hit himself and causing him to lose his power—these are all destined events."
"So, we can start from these destined events and make some slight modifications to the magic protecting Harry, allowing it to have an effect on Lily herself as well."
Speaking of this, he said with a serious face.
"I want to clarify one thing first: when I say 'save Lily', I don't mean she won't die."
Snape's face immediately darkened again.
"Then what's the point of this!"
"The point is huge!" Sherlock said solemnly. "I promised you a two-year timeframe. If I couldn't find a way back within two years, I would help you find a way to keep Lily alive. We haven't reached two years yet, and this method counts as a form of redemption at the very least. You can view it as a fallback plan; even if there truly are no other ways in the end, it's not bad."
Snape was silent for a moment, then he looked up at Sherlock.
"How is your progress at the Ministry of Magic?"
Sherlock sighed and shook his head.
"No progress at all. The research on time in the Department of Mysteries is all related to the past and cannot provide any help. To tell you the truth, I really don't hold much hope about being able to return, but I'm just unwilling to give up and still want to keep looking for a way."
As he said this, he took out the results of his painstaking research from the past few days from his pocket and handed the magic notebook to Snape.
"You have to find a way to give this to her yourself; I can't help with that. Let me remind you once more, Snape: regardless of whether we can go back, even if you really want to change history to save Lily, you had best not make any random changes before everything is properly planned. Even the slightest deviation from the original could have a tremendous impact on the future."
Snape took the notebook from his hand. His gaze was vacant, as if he were pondering Sherlock's words or perhaps thinking about how to get this notebook into Lily's hands without her suspecting anything.
The item had been delivered, and Sherlock had no reason to stay any longer. He stood up, patted Snape on the shoulder, and turned to leave.
Just as he opened the door and was about to go out, a cold voice suddenly came from behind him.
"Thank you."
Sherlock's body paused slightly. He didn't respond, just waved his hand, and then used Apparition to leave the Leaky Cauldron.
In Room 10, the ruined Potion was still bubbling away. Snape looked at the magic notebook in his hand, his knuckles turning white from gripping it too hard.
Those vacant, cold eyes seemed to have ignited a small flame called hope within them.
...
When Sherlock returned to the Department of Mysteries, it was already 11 o'clock at night.
At this hour, the Ministry of Magic had long since fallen into silence, especially in the Department of Mysteries.
Because he was afraid of waking Amy, who was likely already asleep, he didn't choose his office as the landing point for his Apparition, but instead arrived in the black hall.
As soon as he landed, Sherlock sensed something was wrong.
Among the twelve doors on the circular wall, one of the black doors was actually open!
He instinctively frowned and walked with light steps to the black door that had been left ajar.
Having stayed here for so long, Sherlock could naturally distinguish what was behind each of these black doors. The door that had been opened was the Brain Room, a room where there were usually no Unspeakables stationed to conduct research.
Everyone in the Department of Mysteries had their own division of labour, and the Brain Room was an area where no one was conducting research at this time. This door was generally never opened, let alone in the middle of the night.
Sherlock narrowed his eyes and drew his wand. At the same time, he scattered a dozen other wands, which floated around him as he gently pushed open the door to the Brain Room.
It was still as empty as before, with only a table. In the centre, the large glass tank with white brains swimming in dark green liquid was very conspicuous.
They were like jellyfish in the sea, with their thought tentacles floating below, looking completely harmless.
Sherlock's attention was not on these things at this moment; his gaze was fixed on the doors inside the Brain Room.
One of those doors, which previously couldn't be opened, was now slightly ajar, with a visible gap.
This door, which had always been locked, had been opened!
Sherlock's steps were very light as he cautiously walked to that door.
He extended his field of Control Magic, peeking at the things inside the room through the opened door.
He didn't see anyone within his range of perception. The room seemed to be filled with rows of shelves, and on the shelves were silver filaments stored in long, cylindrical glass vials.
After hesitating for only a few seconds, Sherlock made a decision, reached out, and pushed the slightly ajar door wide open.
The door seemed not to have been opened for a long time; the rusty hinges let out a long, creaking sound that seemed exceptionally harsh in the quiet space.
The room was very dark; even with someone entering, no lights turned on by themselves.
"Lumos."
Sherlock incanted the spell, and the wands floating around him all lit up with bright luminescence.
The range illuminated by the dozen Lumos Charms was quite far; everything within a fifteen-metre radius could be seen very clearly.
This room was exceptionally large. Although he couldn't see the boundaries, Sherlock estimated that even the Death Chamber, which was about half the size of a football field, was not as spacious as this.
And looking with his naked eye, he finally saw clearly what those silver filaments stored in glass bottles on the shelves were.
Sherlock had seen things exactly like this before.
The semester when the Chamber of Secrets was opened, Dumbledore took him to see his own past memories; what he extracted from his brain with his wand were these exact same silver filaments.
Sherlock looked around at the thousands of silver filaments on the surrounding shelves; these were all various kinds of memories!
He walked slowly and gently between the shelves. Even though he deliberately kept his footsteps quiet, the sound of his soles touching the floor was still clear.
The wands floating around him also followed his pace, gradually venturing deeper into this room filled with memories.
Just as he crossed another row of shelves and had walked more than ten metres, a rush of footsteps suddenly came from outside the room.
The door to the room storing the various memories was pushed open from the outside again. Madam Selwyn walked in with a look of fury and saw Sherlock, who was venturing deeper inside.
"What are you doing here! Who let you in!"
Sherlock stopped in his tracks and explained.
"The door to this room was already open before I came in..."
However, before he could finish his sentence, Madam Selwyn abandoned her previous gentleness and shrilly interrupted him.
"Get out! I don't care why you came in! Now, immediately, right now! Get out!"
Sherlock had no intention of investigating to the very end; this matter had nothing to do with him anyway. Since Madam Selwyn's reaction was so intense, there was no need for him to stay and continue to invite trouble.
After he left the Hall of Memories, Madam Selwyn nervously patrolled the entire room, which was about the size of a football field. After finding no one, she cautiously touched a spot on the right wall.
Immediately, a wooden cabinet suddenly popped out from the smooth wall, which had shown no signs of any gaps. Inside were memories identical to those glass bottles on the shelves.
She carefully counted the number of those memories, and after confirming that none were missing, she let out a long sigh of relief.
Returning the secret compartment to its original place, Madam Selwyn left the Hall of Memories and locked the door from the outside with special magic.
The Hall of Memories fell into darkness once again.
After Madam Selwyn left, it was quiet for another ten minutes. Then, a thin figure lightly jumped down from the ceiling; the sound of landing was exceptionally clear in the empty room.
The spot where he was hiding was located about eleven or twelve metres further in from where Sherlock had walked to the deepest point.
If Madam Selwyn hadn't appeared suddenly to drive him out, Sherlock would have taken two more steps forward, and his extended Control Magic would have been able to perceive the presence of the person hiding on the ceiling.
Unfortunately, that possibility would no longer arise.
The thin figure walked quickly to the wall on the right side of the Hall of Memories, found the spot Madam Selwyn had just touched, and also pressed down lightly. Immediately, the secret compartment containing certain special memories popped out once again.
The silver light shone on the young face of the figure. He extended his slightly trembling hands, which appeared somewhat excited, and took all three bottles of memories labelled "Clark Selwyn", putting them into his pocket.
Then, he drew his wand and used Apparition to leave the Hall of Memories, which had been sealed from the outside.
And everything he did went unnoticed by anyone.
The next day.
Madam Selwyn came to Sherlock's office and found him.
"Apologies, I was a bit agitated last night, Watson."
Although she was apologising, switching to his surname instead of his first name already showed her coldness.
Sherlock waved his hand.
"It is I who should apologise to you, Madam. Seeing that the door to that room was open, I should have informed you immediately instead of going in to investigate myself."
He said this on the surface, but if he were to actually do that, he would truly be brainless.
Madam Selwyn frowned tightly.
"That door wasn't opened by you?"
The distrust revealed in her tone was audible to everyone, and Sherlock sighed deeply in his heart.
With this suspicion once planted, his future actions in the Department of Mysteries would not be as convenient. Going to research other things would likewise be labelled as having ulterior motives.
"I truly did not do such a thing, Madam. Entering that room, I was also just trying to find the person who opened the door."
Madam Selwyn nodded slightly and said flatly.
"Perhaps that is the case. However, in the future, refrain from asking about matters outside of time research; just focus on your own work."
"Very well, Madam."
Sherlock nodded.
At this moment, he was already starting to consider leaving the Ministry of Magic.
From what he understood now, these magic researches in the Department of Mysteries were of no help at all to his goal of returning to the correct timeline.
And Horcrux magic was an unexpected gain.(TN: Why call it Horcrux magic of all things?)