Students were forbidden from wandering the halls at night in Hogwarts.
At this hour, when Sean slipped out of the Slytherin common room, he normally wouldn't encounter other students—only Filch or perhaps a professor on patrol.
But tonight Sean had the Marauder's Map.
Even if Filch came out to patrol, Sean could track his movements on the map and avoid him easily.
Quietly, Sean slipped out of the Slytherin common room.
According to the map, the corridors were empty. The professors were all inside their rooms, while Filch was patrolling on the first floor.
Sean quickly made his way to the advanced Potions classroom on the eighth floor.
He pointed his wand at the keyhole.
"Alohomora."
The wooden door opened with a soft click.
Sean pushed it open carefully and slipped inside before closing it behind him.
There were only a dozen workstations in this classroom.
Very few students took Advanced Potion-Making.
Snape had strict requirements: only students who achieved Outstanding on their fifth-year Potions O.W.L. exam were allowed to continue into N.E.W.T.-level Potions.
Sean cast a small light spell toward the cabinets at the back of the room.
"Lumos."
He began searching through the cabinets one by one.
The book he wanted should be old—very old.
After rummaging through the first cabinet without success, he moved to the second.
Starting from the top drawer, he worked his way down.
When he opened the second-to-last drawer, he felt a spark of anticipation.
"Advanced Potion-Making," Sean murmured.
There were two copies inside.
One looked worn and battered.
The other looked relatively new.
Sean picked up the old one and opened the first page under the glow of his wand.
There it was.
A signature.
"The Half-Blood Prince."
"That's the one."
Sean had successfully found the Potions textbook once used by Snape himself.
This discovery dispelled a theory Sean had previously considered.
For a time, he had suspected that Harry obtaining this book had been orchestrated somehow.
Now it was obvious that Harry had gotten it purely by chance.
During Snape's tenure, only students who achieved Outstanding on their Potions O.W.L. could continue to N.E.W.T.-level classes.
No one knew what Harry's result would be beforehand.
In fact, Harry had only received an Exceeds Expectations.
Technically, he shouldn't have qualified for Advanced Potion-Making at all.
Because of that, Harry never prepared the textbook over the summer.
If Harry had achieved an Outstanding, he would have bought the book himself.
Later, Professor McGonagall suddenly informed Harry that the new Potions professor—Horace Slughorn—had relaxed the requirements.
Students with Exceeds Expectations could now take the class.
So Harry and Ron went to the class unexpectedly.
Neither of them had the textbook.
Slughorn told them to grab spare copies from the cabinet.
Inside were two books—one old and one newer.
Naturally, neither boy wanted the battered one.
They fought over the better copy.
Ron won.
Which meant Harry ended up with the old textbook.
"Snape really is a genius when it comes to potions," Sean said quietly as he flipped through the pages filled with handwritten notes and corrections.
When he reached the later pages and saw Snape's own invented spell—Sectumsempra—Sean felt genuine admiration.
"No… he's a genius in spellcraft too."
At sixteen years old, Snape had already been modifying textbook instructions, optimizing potion recipes, and inventing entirely new spells.
He truly was extraordinary.
"To Hogwarts students, this book would be a treasure," Sean thought.
"But to Snape, it was probably just one of many school notebooks."
Which was probably why he had left it in this classroom.
Someone as meticulous as Snape would never casually discard something truly important.
Sean planned to copy the book by hand and return it afterward.
After all—
Harry would need it in the future.
Just then, Sean glanced at the Marauder's Map.
Four sets of footsteps were approaching the classroom.
Just a minute earlier, the corridor had been completely empty.
Sean stared at one of the names.
"Nymphadora Tonks… that name sounds familiar."
He extinguished his light and hid behind a bookshelf.
In the dim moonlight from the window, he watched the footprints on the map pass by.
Only when the two figures moved away did Sean stand up again.
Then something clicked in his mind.
"Nymphadora… right. That's her."
"The woman who eventually marries Lupin."
Sean couldn't help feeling sympathy for that couple.
They fought through countless difficulties to be together, only to die together during the Battle of Hogwarts.
"I always imagined she was older since she married Lupin," Sean muttered.
"But she's still a Hogwarts student right now."
Sean had assumed too much.
Lupin had been in the same year as Harry's father.
Meanwhile, Nymphadora Tonks would currently be a sixth- or seventh-year student.
Their future marriage would actually have quite a large age gap.
When Sean left the Potions classroom and walked down the corridor toward the Slytherin common room, something suddenly struck him as strange.
"Wait… something's not right."
"Tonks wasn't on the map earlier."
He stared at the Marauder's Map thoughtfully.
"How did she appear out of nowhere?"
"Did she somehow hide her magical presence? That can't be right. Even Filch shows up on the map."
Sean stopped walking.
His eyes drifted toward a tapestry on the wall.
It showed a troll swinging a club at a man.
Then realization struck.
"The Room of Requirement."
"How could I forget about that?"
He looked at the blank wall opposite the tapestry.
At the moment, it was just a wall.
But if someone walked past it three times while focusing on what they needed, a smooth door would appear.
Behind that door would be the Room of Requirement—a magical chamber that even the Marauder's Map could not detect.
"Perfect," Sean whispered.
"I can practice magic there in the future."
The room could transform itself according to the user's needs.
If someone needed a bathroom, it could even produce a toilet.
Just then, Sean noticed Filch's footsteps on the map moving toward this corridor.
Sean considered it for a moment.
He had already obtained Snape's textbook tonight.
The Room of Requirement could wait for another time.
After returning to the Slytherin common room, Sean noticed an older student sitting on the sofa in his pajamas.
When Sean approached, the student stood up.
"Where were you?"
"Couldn't sleep. Went for a walk," Sean replied calmly.
"Students aren't allowed outside the common room at night," the older student said coldly. "Are you trying to make Slytherin lose points?"
"If we lose points, I'll earn them back," Sean said casually.
The older student's eyes turned hostile.
"Sean Grylls. Don't think a little cleverness gives you the right to be arrogant."
"Slytherin doesn't welcome traitors like you."
Sean understood immediately.
Another pure-blood wizard who despised his family background.
Sean was almost certain—
this guy's family was either filled with Ministry officials…
or Death Eaters.