Harry followed George and Fred into an empty classroom nearby.
"Why didn't you go to Hogsmeade?" Harry asked, puzzled.
George and Fred exchanged glances, then said with mysterious grins.
"Because we decided to give you an early Christmas present, Harry. We'll leave once we've given you this gift."
As they spoke, Fred pulled a tattered piece of parchment—the Marauder's Map—from his pocket.
Then they taught Harry how to use it. Harry was stunned as he looked at the map, which recorded all the routes in Hogwarts and also showed the movements of everyone in the Castle.
George was still explaining the rules for using the map to him.
"Remember, don't let any teacher see this map, except for Professor Cavendish."
Harry snapped back to attention at his words and asked, confused.
"Why can Professor Cavendish know?"
"Because last year, Professor Cavendish already knew about the Marauder's Map," Fred said with a shrug.
George continued his explanation. "Yes, it was the first day of school. We had just pranked Filch, who was waiting to catch us. As we were sneaking out of the Gryffindor Common Room and opening the Marauder's Map, we saw Professor Cavendish staring at us by the door."
Fred shivered slightly, recalling that terrifying scene.
"We were so scared when we saw the Professor that we even forgot to hide the map, and then the Professor took it away."
"But Professor Cavendish still gave us a chance. He promised to return the map to us as long as we behaved well."
"Yes, that period was almost the most well-behaved time George and I had ever been at school," Fred said with emotion. "If Mum had seen us, she would have been very pleased and thought we'd changed for the better."
"Although the Professor extended the time a bit, he still returned the map to us at the end of the semester."
"However, before he returned the map to us, it seemed as though he used some magic on it to remove his name."
Hearing them say this, Harry realised that Sherlock's name was indeed missing from the Marauder's Map.
George patted him on the shoulder.
"It only lacks Professor Cavendish's name, but it's still very useful. We don't need it anymore, so we decided to give it to you!"
The two of them handed the Marauder's Map to Harry, then bid him farewell and prepared to go to Hogsmeade through the main gate.
Harry looked at the Marauder's Map in his hand, and his eyes gradually lit up.
Although he had endured many lectures from Sherlock, Harry's restless heart would not be easily changed.
He had always envied the others who could relax in Hogsmeade Village at the weekend, while he had to stay in the Castle alone.
And now, his chance to slip out was finally here.
The Marauder's Map recorded all the secret passages from Hogwarts to Hogsmeade, allowing Harry to leave with ease.
There was an entrance to a secret passage behind the humpbacked one-eyed witch statue where he was currently standing.
With excitement and a hint of guilt in his heart, Harry walked into the secret passage.
But this trip to Hogsmeade was not as pleasant as he had imagined.
Just as Harry was heading to Hogsmeade through the secret passage, Sherlock gently knocked on the door of Snape's office.
After a gloomy voice from inside said, "Come in," Sherlock pushed the door open and entered.
Even with Christmas approaching, Snape was not idle. A cauldron was boiling over a fire in front of him, and the Potion inside was bubbling with steam.
Upon seeing that it was Sherlock, Snape's expression showed some surprise, and a mysterious smile played on his lips.
"What do you want from me?"
Sherlock didn't care about Snape's mood. He pulled a list from his pocket and placed it on the desk.
"I need these ingredients. Of course, I won't take them for free; I'll pay the normal price."
Snape picked up the ingredient list from the desk.
Sherlock had not concealed anything about the Potion ingredients. With Snape's discerning eye, he could naturally tell what Potion Sherlock was preparing just by looking at the ingredients.
"Billywig stings, Doxy secretions, dittany picked under the full moon... You want to brew a Sorrow Potion?"
Sherlock neither confirmed nor denied it.
"So, do you have these ingredients?"
Snape looked at him arrogantly, his gaze still vacant and cold, his hair hanging down as though it had been oiled and not groomed for a long time.
"Ah, how difficult, Cavendish, that you've come begging to me. You need three sets of these ingredients. As a colleague working at the school, how about I charge you fifty Galleons?"
Sherlock looked at him with disdain.
"You're really greedy."
"Do you want them or not?"
Sherlock took out his money pouch from his pocket and placed it on the table.
"Here are thirty Galleons. I'll give you the remaining twenty next time."
These ingredients were not actually worth that much money, but some of them were difficult to buy in the Wizarding World, not because they were rare, but because it was not the season for them to be used. It was likely only Potion Masters like Snape who would have them in stock year-round.
So, even if he was charging more than the normal market price, as long as it wasn't too excessive, Sherlock would simply accept it.
Snape retrieved three sets of Sorrow Potion ingredients from his stores for Sherlock. Just as Sherlock took the ingredients and was about to leave, Snape suddenly called out to him.
"Don't you want to know what Potion I'm brewing?"
Such an attempt to entice someone into continuing the conversation was rare coming from Snape.
Sherlock stopped, turned back, and carefully looked at the boiling Potion in the cauldron. After a moment of thought, he knew what Snape was trying to do.
A slight smile appeared at the corner of his lips, so he was no longer in a hurry to leave and sat down in a chair in Snape's office.
"Oh, I'm sorry, I don't have as deep an understanding of Potions as Master Snape, but perhaps I do know a little."
Sherlock pretended to study the Potion.
"If I'm not mistaken, this should be a Wolfsbane Potion, right?"
Snape's tone hinted at impatience.
"Indeed. The effects of this Potion are quite uncommon."
"Uncommon indeed." Sherlock nodded. "While it can't completely cure a werewolf, it's enough to be called a saviour for them."
Snape's impatience was now undisguised.
"Yes, a werewolf's saviour. So if everyone in the Castle were normal, why would I be brewing this Potion?"
Sherlock shrugged.
"How would I know?"
Snape's expectant expression instantly froze, and his face darkened.
"Can't you use your brain for once and think!"
If this had been before he transmigrated, Sherlock would have pointed at his face and mocked him: He's getting anxious, he's getting anxious.
But now he was in Snape's office. If he really said that, tomorrow's headline in the Daily Prophet would probably be—The Sorrow of Magical Education: The Truth Behind Two Hogwarts Professors Fighting.
"I'm very busy every day and don't have the time to think about such things. Why don't you just tell me the answer directly, Snape? Tell me why you're brewing this Wolfsbane Potion," Sherlock said unhurriedly.
Snape coldly watched Sherlock's feigned ignorance. He was no fool and naturally saw through the act.
"You actually already guessed?"
Seeing that he had been found out, Sherlock no longer pretended.
"Thanks to your reminder. You went to great lengths to talk so much about werewolves during your substitute classes."
Snape stared at him.
"Since you know, why don't you expose his true colours? Don't you think having a werewolf at Hogwarts is a danger to the students?"
Sherlock scoffed.
"You knew even earlier than I did. Why didn't you expose him yourself instead of dropping hints and making me the scapegoat?"
Snape seemed to be gritting his teeth, though his expression revealed little of his resentment.
"I promised Dumbledore I would keep this a secret and tell no one."
"You've already broken your promise. Even if it's only a subtle hint, it's still a hint, and you've made me an accomplice."
Sherlock suddenly looked at him curiously.
"By the way, what kind of grudge do you have against Lupin? He seems like a decent person. Why do you hate him so much, wishing for his identity to be exposed and for him to be expelled from Hogwarts? Is it jealousy over the Defence Against the Dark Arts Professor position? No, that's not right. He's only an assistant teacher. If you're going to be jealous, you should be jealous of me."
The Potion continued bubbling in the dimly lit office. Snape stood motionless, his hands tightly clenched into fists.
"A decent person? Is that really what you think of him?"
He did not furiously throw Sherlock out or coldly tell him to leave.
"Do you know what he almost did back then? He turned into a werewolf, and his friends lured me there, trapping me in the same room with him while he was transforming! If it hadn't been for one of them losing his nerve at the last moment, afraid of being expelled because of my death, and letting me out, then Severus Snape wouldn't be standing before you now!"
Snape gazed at Sherlock. His words were not especially emotional or angry, but the hatred woven into them was unmistakable.
Sherlock was stunned by what he heard. He had never expected Snape and Lupin to have such a deep grudge.
He had previously thought Snape was simply petty, holding on to some trivial slight from their school days until now.
Judging solely from the incident he had just described, his hatred of Lupin was not without reason.
Sherlock sighed, no longer in the mood to tease Snape.
"Even if he almost killed you back then, it wasn't intentional. Once he transforms into a werewolf, he loses consciousness. If you're going to hate anyone, you should hate the people who tricked you into going there."
Snape said coldly,
"What's the difference? Just because he was unconscious when he almost killed me, I can't hold a grudge against him? Can you really be that magnanimous?"
Sherlock was speechless.
He had originally intended to mediate the conflict between Snape and Lupin, but it now seemed utterly irreconcilable.
Their past was certainly far more complicated than Snape had described. With such a tangled history, Sherlock no longer felt like arguing over who was right or wrong, and he left with the Potion ingredients.
Just as Sherlock, lost in thought, reached the door of his office, he noticed a familiar figure standing there.
A black robe enveloped her entire body, and a wide hood covered most of her face, leaving only the lower half exceptionally pale.
Sherlock looked at Hilke, who was waiting at the door, and said in surprise,
"I thought you were lying to me before and wouldn't come back. You really didn't just leave me here?"
Hilke ignored Sherlock's banter and said coolly,
"I found some somewhat useful information, but only somewhat useful."
Sherlock opened the office door and walked in with Hilke.
He sat down in his chair and pulled the locket from beneath his robes.
"So what exactly is this thing?"
Hilke calmly recounted what she had learned from her trip.
"The Department arranged for me to meet an old Goblin who has been alive since the Goblin Rebellions. He told me that during the darkest period of the war, the Goblins once considered the possibility of defeat."
"They deliberated together and, based on the situation at the time, gathered several of the greatest Goblin craftsmen to create an alchemical item that could turn the tide after their defeat. They hid it in the deepest secret command centre underground."
"But for some reason, after the Goblins lost the war, they never activated this alchemical item. The Goblin I spoke with was not one of the leaders at the time; he had only heard rumours of its existence."
"It is widely believed among Goblins that it represents the pinnacle of Goblin alchemy over the past thousand years, but what it looks like and what it was actually meant to do died with the Goblins who knew the truth."
Sherlock looked at the unremarkable locket, never expecting it to represent the highest achievement of Goblin alchemy.
After hearing everything Hilke had learned about the locket, he could not help wondering,
"If this is the alchemical item the Goblins created to turn the tide of the war, how did that scarecrow know about it? And what was he planning to do by finding it?"
Hilke shook her head.
"I don't know, but that's what the Department is investigating now. They're trying to get some answers from Fedetick."