Sherlock hadn't considered whether he could catch the mastermind, but he thought the possibility of finding the old book was still very high.
He hadn't forgotten the previous anomaly he noticed in a certain student; now he at least had a target for suspicion.
"Password?"
The portrait of the Fat Lady in front of the Gryffindor common room entrance yawned and asked Sherlock perfunctorily.
She had already been informed that professors would be searching the common room, and asking for the password was just a formality.
"Dragon dung."
After he gave the correct password, the portrait of the Fat Lady opened the common room entrance, allowing Sherlock to enter.
When introducing the newly arrived students, the prefects of every house would boast that their common room hadn't been entered by outsiders for hundreds of years.
Sherlock felt that these claims were likely false.
Although the entrances to the four house common rooms were guarded in different ways, if a wizard truly wanted to enter, these simple defences couldn't stop them.
Just like him now, with Dumbledore's permission, a Ravenclaw graduate walked openly into the Gryffindor common room.
Sherlock didn't have a strong desire to pry; he wasn't interested in what the students might have hidden in their dormitories.
After entering, he went straight to the boys' dormitory; Professor McGonagall would handle the search of the girls' dormitory.
Even the restless Gryffindors didn't have very messy dormitories.
This wasn't because the little lions were particularly diligent, but because hardworking house-elves helped them clean every day.
Searching the dormitory wasn't too much trouble; after entering, Sherlock only needed to lightly wave his wand and use Accio to summon all the books in the room to him.
After checking that everything was fine, he would simply let all the books fly back to their original places.
But after entering a room that looked exactly like the others, Sherlock's attention suddenly became highly focused.
He saw the signatures on the parchment papers lying on the desk.
This was Harry and Ron's dormitory.
However, his focus was not on Harry or his friends.
Just like in the other dormitories, after first using Accio to check all the books in the room and finding no issues, he specifically walked over to the four-poster bed marked with Neville Longbottom's name and meticulously inspected all of Neville's belongings.
The result was that he found no anomalous items.
Sherlock frowned. He checked everything related to Neville in the dormitory again, but the result remained the same.
Ultimately having found nothing, Sherlock had to leave the Gryffindor common room. After checking the Ravenclaw boys' dormitory, he also found nothing.
At eight o'clock in the evening, the four professors responsible for the search gathered in the corridor in front of the Great Hall.
"I didn't find anything on my end," said Professor Sprout, who had searched the Slytherin and Hufflepuff girls' dormitories, shaking her head.
It went without saying for the rest; Sherlock could tell from the expressions of Professor McGonagall and Snape that they hadn't found anything either.
He rubbed his chin and turned his gaze towards the entrance of the Great Hall.
"Let's check on the students first. The student who was being misled might have been carrying the book with them the whole time."
The professors all turned their attention to the Great Hall entrance. Indeed, this was the most likely possibility now.
They walked into the Great Hall. Professor Flitwick had just finished counting all the students in the Great Hall, cooperating with Filch.
Confirming that everyone was present, except for the three students who had been attacked and were currently lying in the Hospital Wing.
There were now five professors gathered in the Great Hall.
The four house heads, plus Sherlock, the Defence Against the Dark Arts professor, who held a special position at Hogwarts.
The students were separated by house, and the dean of each house was responsible for checking their own students.
Of course, outwardly they didn't say they were searching for an old book, but rather observed each student discreetly.
Sherlock had previously come into contact with that old book; it wasn't very thin, and if someone were constantly carrying it, it would be clearly noticeable, especially since most students were currently wearing pyjamas.
Sherlock, with a clear objective, went to the Gryffindor seating area and found Neville sitting alone on the floor, staring blankly.
"Mr. Longbottom."
Neville heard Sherlock's voice and his body gave a start. He looked up, slightly flustered.
"P-Professor Cavendish."
Seeing his reaction, Sherlock further confirmed the suspicion in his heart.
Neville definitely had something wrong!
After tracing the clues in the Headmaster's Office, he had realised that what caused the reaction in the mark on his left arm at the bookshop was likely not the Malfoy father and son, but that old book.
After arriving at Hogwarts, this burning reaction happened again, this time on Neville.
This forced Sherlock to link the two events together.
"Mr. Longbottom, can you tell me where you were when Malfoy was attacked?"
Sherlock asked flatly.
However, his gaze did not meet Neville's; instead, he was scrutinising the items Neville was carrying.
Neville looked very nervous under his questioning, stammering out:
"I, I was with Seamus and the others at the time, in the d-dormitory, doing Potions homework."
Before Sherlock could ask again, Seamus, who was nearby, spoke up voluntarily.
"Yes, Professor, I can vouch for Neville!"
Where Neville was when Malfoy was attacked wasn't important; a basilisk didn't necessarily need its master watching nearby to launch an attack. Sherlock only asked this as a casual excuse to strike up a conversation with Neville.
But the result disappointed him once again.
Neville had already changed into his pyjamas; there was nowhere on his person to hide anything, let alone such an obvious old book.
Having gained nothing, Sherlock didn't press further. He was also worried about alerting the enemy; if that old book got agitated and caused a major incident at Hogwarts before slipping away, it would be troublesome.
The inspection of the students quickly finished. The five professors gathered together again; none of them had found anything.
Professor McGonagall's expression was grim. She turned and left the Great Hall.
"I'm going to find Albus to see if he has any other ideas."
Professor Sprout sighed and shook her head.
"I'll go tell the students to go to sleep."
Professor Flitwick went with her, leaving only Snape and Sherlock standing on the raised platform, watching the students below who, following the instructions of the two professors, were climbing into their sleeping bags to prepare for sleep.
"The results were not as you predicted," Snape said coldly.
Sherlock was also frustrated, and he retorted coolly.
"If everything went exactly as I thought, then I wouldn't be a wizard; I'd be a god, as the Muggles call it."