After sending the letter, Lin Du did not simply sit back and wait for death.
Using his status as a professor, over the next few days, he conducted a thorough yet discreet search of Hogwarts with Chao Feng under the pretext of "familiarizing himself with the castle's security layout."
He investigated nearly every known abandoned classroom, behind suspicious statues, and even used magic to probe the hollow spaces behind walls and the paths of the pipes.
The result was nothing.
Slytherin's Chamber of Secrets seemed never to have existed, leaving behind no magical traces that could be followed.
Although Chao Feng could vaguely sense that cold, evil power flowing through the pipes, it could not pinpoint its source, as though some powerful ancient magic was interfering and concealing it.
"It's like hunting a shadow in a maze." Lin Du stood at the end of an empty corridor and murmured to Chao Feng, who was perched on his shoulder.
He tapped what appeared to be an ordinary wall beside him. All it gave back was a dull, solid thud.
"Slytherin's methods aren't that simple." Chao Feng flicked its tail. "Unless that 'heir' acts again and opens the Chamber of Secrets himself, it'll be difficult for us to find the entrance."
Lin Du fell silent for a moment.
Passive waiting was not his style, especially in the face of potential danger.
Since he could not solve the problem at its source for the time being, he had to strengthen their ability to handle a crisis.
"Looks like it's time to change the focus of my teaching." A trace of resolve flashed through Lin Du's eyes. "Theoretical foundations are certainly important, but what Hogwarts students need most right now is practical combat experience."
Chao Feng, still on his shoulder, glanced at him and sent over a teasing voice.
"Tsk, since when did you become so concerned about the students? Why do I get the feeling you're holding back some nasty scheme and looking for a legitimate excuse to 'temper' them?"
Lin Du remained expressionless. "Maximizing their chances of survival in potential danger is the duty of a Professor of Defense Against the Dark Arts. As for whether they feel 'pain' in the process, that is not within my consideration."
"How high-minded." Chao Feng scoffed, but did not argue further. It knew there were more practical considerations behind Lin Du's decision.
Thus, in the following Defense Against the Dark Arts classes, the students discovered in horror that Professor Lin Du's teaching style had undergone an earth-shaking change.
"Put your textbooks away." On Monday morning, Lin Du stood before the fourth-year Ravenclaw and Hufflepuff students, his tone leaving no room for dispute.
"Starting today, we will be conducting practical application training. Theoretical assessments will account for only thirty percent of your final grade."
A wave of suppressed groans rose in the classroom.
"Quiet." Lin Du tapped his wand lightly, and several large words appeared on the blackboard: [Practical Responses to Dark Magic Creatures].
"Hogwarts is safe, but that does not mean the world you will face in the future will be equally safe. The O.W.Ls do not merely test what you know; they test what you can do with what you have learned. And I hope you survive the exams—and survive any danger you may encounter in the future."
His words were like a basin of ice-cold water, splashing over every student without warning.
The practical training was arranged in an empty classroom on the fourth floor that had been specially modified.
When the first class lined up in a long queue in the corridor, they all whispered uneasily among themselves.
Powerful Concealment Charms and Space-Expansion Charms had been cast around the classroom door. Nothing could be seen or heard from outside.
"The content of this class is very simple." Lin Du looked at the nervous students before him, his voice reaching every ear clearly.
"I will simulate several attack scenarios involving Dark Magic creatures that may appear in the O.W.Ls or be encountered in the wilderness. You will need to use the knowledge you have learned over the past few years to assess the situation, cast the appropriate spells, safely clear the challenge, or subdue the target."
"How is it? Very simple, isn't it?" He even smiled slightly, but that smile sent chills down the students' spines.
Simple? It sounded terrifying enough already!
Who knew what was waiting for them inside? An upgraded version of Cornish Pixies? Or something even more horrifying?
"Miss Brown." Lin Du pointed at a pale-faced Ravenclaw girl. "You're first."
The girl tremblingly raised her wand, took a deep breath, and pushed open the classroom door. The door closed behind her, leaving the students outside to wait anxiously.
Ten minutes later, the door opened, and the girl named Brown emerged. More than half of her robes were soaked, several strands of pondweed clung to her hair, and her face was pale, but her eyes shone with astonishing brightness.
"I... I did it!" she said excitedly to her companions. "There was a pond inside, with a Grindylow! I used a Freezing Charm to freeze part of the surface, then ran across quickly!"
Her success gave those behind her some courage, but after that, the second and third students who entered either failed and were brought out early by Lin Du, or barely made it through in a miserable state.
The scenes in the classroom seemed to change at random. Sometimes it was a dark forest environment for dealing with Red Caps; sometimes it was a narrow tunnel for dealing with Kappas. But the most troublesome one was that strange pond.
When it was the fourth-year Gryffindors' turn, the most conspicuous people in the line were undoubtedly the Weasley twins—George and Fred.
Although the previous night, they had nearly let the caretaker, Mr. Filch, experience "feet stuck in mud" while testing some sort of "portable swamp" in one of the castle corridors, and had been caught red-handed by Professor McGonagall and given a hefty detention, it seemed not to have affected their spirits in the slightest.
The two still winked and pulled faces in the queue, quietly exchanging guesses about what was happening inside the classroom, as though they were about to embark on an interesting adventure rather than face a dangerous practical test.
"Mr. George Weasley," Lin Du said calmly as he watched the two trying to switch identities, "or Fred? If you cannot determine who is who, I would not mind asking Professor Flitwick to come help identify you. I'm sure he would be delighted to give you extra tutoring in Charms."
Under the threat of "extra tutoring," George finally stepped forward with a miserable expression, holding his wand as he walked into the classroom like a man marching to his death.
The moment he entered, the pond radiating a damp chill blocked his path.
The pond did not look deep, but its water was murky and greenish, making it impossible to see what lay beneath the surface.
Lin Du followed behind him, his gaze sweeping across a spot on the water where a sickly green creature with horns—
A Grindylow—was extending and retracting its long claws in George's direction.
George cautiously slid into the water, and the icy pond water made him shudder.
He tried to swim across quickly, but immediately felt a powerful resistance, as though he had fallen into a swamp.
"Swamp Curse..." George understood at once. He slowed his movements, and the resistance indeed weakened.
He smugly pulled a face in Lin Du's direction.
However, just as he lowered his guard and thought he had grasped the trick, an icy, slimy hand suddenly seized his ankle!
George was horrified. He instinctively struggled with all his strength, and the moment he did, the Swamp Curse's effect intensified, leaving him almost unable to move.
He tried to pull out his wand and point it underwater, but the moment he opened his mouth, frigid pond water rushed in. All he could release was a string of helpless bubbles.
Underwater, the Grindylow grinned viciously as it dragged him deeper.
Lack of oxygen turned George's face bright red, and fear seized him.
Just as he was about to give up, amid the chaos, his foot kicked wildly and unexpectedly struck the Grindylow hard in the head!
The injured Grindylow released its claws.
But because of his violent struggle, George was trapped even deeper by the Swamp Curse and lacked the strength to rise to the surface.
Outside the classroom, only three minutes had passed.
Watching the bubbles on the surface steadily diminish, Lin Du shook his head and flicked his wand. A rope lying on the bank shot into the water like a living snake, wrapped precisely around George's waist, and swiftly dragged him out.
"Cough! Cough, cough, cough..." George dropped to his knees and coughed violently, spitting out several mouthfuls of pond water, his face pale.
Lin Du tapped him on the back with his wand. An efficient Drying Charm instantly dried his robes, after which Lin Du handed him a small bottle of pungent Draught of Living Death.
George pinched his nose and gulped it down, feeling a warm current spread through his body. His coughing immediately stopped.
He raised his head and looked at Lin Du aggrievedly. "Professor, this... this is way too dangerous, isn't it?"
Lin Du glanced at him. "A real Grindylow would not let go so easily just because you kicked it once, and they usually move in groups. Remember this lesson: when facing threats underwater, staying calm is more important than any spell. Gryffindor loses five points for your recklessness and lack of preparation."
George opened his mouth, but in the end, he dejectedly followed Lin Du out of the classroom.
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