The Restricted Section
Harry reached his dorm within a few minutes and flung on the invisibility cloak, still trying to dispel the pleasant cotton-like feeling. As he hurried back down to the first floor so he could enter the library, he practiced walking under the Cloak without tripping or letting his feet show, which he really should have done already.
In the library, Madam Pince was sitting at her desk, apparently repairing a torn book with needle and thread. Why didn't she use a repairing spell? As she worked, though, he realized that the book was struggling trying to escape from her ministrations. The book was alive! A repairing charm wouldn't work on it, clearly, and healing spells were made for people, not books, so she had to use muggle methods. Perhaps, Harry realized, her job was not as simple as it seemed.
Harry shrugged under the silky mantle, though, and passed her by. It was a strange feeling to be invisible; not only did he not appear in reflections, but he couldn't see his feet or hands. And people paid him no attention at all; their eyes didn't track him, but stared straight through his body. Harry might have been discovered if Filch hadn't stopped when Peeves made a loud ruckus in another part of the castle. Harry took the opportunity and escaped. Paintings, too, couldn't see him; they did whatever strange things they did when they truly were alone. He had passed a painting of a Minister of Magic picking his nose.
Harry glanced around at the faintly glowing brass plates that identified each row of books. Was he coming the right way? He was sure that the Restricted Section was this way… and what was up with the black splotch on the wall?
Harry stared at the blackness, and a cold wind seemed to billow up from within in, rustling the folds of the Cloak and making the faint lights within it dance. Oh, right, that was the Restricted Section. It was so dark he hadn't noticed it. Odd.
Harry shivered as he descended the black stairs. The pressure on his skin, the warm, comfy feeling of magic that pervaded Hogwarts, was changing. It still pressed against every bit of his body, but the warmth was disappearing, being replaced with a cold, clammy feeling. This must be the reason for the cold winds that blew up the stairs. As he climbed down farther, deep below the castle, Harry realized that the changing feeling of magic – due to Dark magic, he guessed – wasn't abstract. It seemed to be focused on him, an intruder, as it wasn't constant and calm, like Hogwarts' magic was. It pulsed at him, swirled angrily on his skin, and somehow gave the impression that this area – or something in the area – hated him, personally.
It was probably just that he was the only one down here, Harry reasoned, but he still didn't like it, and he resolved to find his book and get out as soon as possible.
Harry glanced over the much smaller Restricted Section of the library. Where the normal library was huge, taking up all of the first floor that wasn't the Great Hall, the Restricted Section was only a single room. It was indeed full of bookshelves, but not all were full; some half-full, some with only a single, fat, smug-looking book in the center. There was one shelf which seemed to be empty, but shimmered like water; another shelf was lined with lead, with a green-glowing tome in the center; there was a steaming basin of ice sitting at one wall with an enticing, hot pink grimoire resting in it. One volume was solid black with stars scattered across it, twinkling gently. Harry was pretty sure he saw a blood-stained tome labeled The Necronomicon.
Harry shivered as the Dark magic that coiled around the room pulsed once more, and he quickly looked up and down the shelves, searching for the book he wanted. But the labels on the shelves were useless: Book of Slow Demise, read the plaque upon the lead-lined shelf; by Herpo the Foul, declared another shelf; Soul Magics, claimed one of the empty shelves. Harry walked hopefully up a shelf which claimed to house books on history, but to no avail. One of them seemed interesting, the True Story of the First Goblin War, but as he opened it the noises of battle sprang from its pages. Harry quickly slammed it shut before anyone could hear.
Finally, Harry found the book he sought, in a row that positively rang with Dark magic, which had been labeled with the uninformative Dark Secrets. Wisdom of the Wizengamot was a slim volume, only a hundred pages at most, describing the lives of the thirteen Lords who had been part of the Wizengamot at the time of writing twenty years ago.
Harry flipped it open to the table of contents, scanning down just the last names, and was glad to see that each section had a title to go along with the name of the Lord. That might help.
Lady of Law
Riddle: Founder's Heir
Dumbledore: Wonderful Wizard
Flamel: Alchemist Supreme
Harry grinned as he read the last line, then nearly vomited as a fresh wave of loathing from the Dark rolled over him. He practically shoved the book into the shelf again as he fled the Restricted Section, but he had found what he was looking for.
Nicholas Flamel had been an Alchemist.
Harry began to slow as he finally reached the first floor, finally exiting the Restricted Section and reentering the main library. He sighed heavily and glanced around, still invisible. No-one was around.
Harry walked as calmly as he could through the dark library, navigating slowly through the entrance. He slipped past Madam Pince easily as the wrinkled librarian struggled to corner a thick book which had apparently been dropped into water; the back half was soaked.
"Calm down!" she shouted at it. "You know you need this appendectomy!"
Harry struggled not to laugh as he peered out the door to the library. Look to the left, empty. Look right, Filch. All clea–
Harry gasped and scrambled back as Filch turned to enter the Library. The ugly old caretaker moved surprisingly quickly, though, and bumped into Harry's elbow.
"Eh?" he asked, swinging his lantern around and nearly walloping Harry. "Who's there?"
Harry froze in place under the Cloak as the caretaker glared about. Then Filch's eyes locked onto something on the ground.
The edge of his robe was protruding out of the Cloak. He quickly tugged it under, but it was too late. Filch had seen.
"Student out of bounds!" the caretaker roared, leaning forward and trying to grab Harry in a bear hug. "Invisible student in the library corridor!"
Harry fled the cursing caretaker, turning corridors wildly and occasionally looking back. Mrs. Norris had arrived and was dashing towards him; the cat must be able to smell him or something. Filch was following her, still bellowing.
Harry ducked into a room around a corner and pressed his wand up against the frame, whispering "Colloportus!" There was a click as the spell took hold, locking the door. He tried to breathe quietly.
"Behind this door, my dear?" Filch rattled the handle of the door, then tried to turn it. "Locked again! You're losing your touch, Mrs. Norris!" Harry heard the caretaker stomp away. Mrs. Norris mewled a few times, but then she too left, claws clicking on the stone floor.
With a deep sigh of relief, Harry glanced around the room he had taken refuge in. It seemed to be a potions lab of some sort. There was dust everywhere; with the practiced eye of someone who had been forced to clean rooms for most of his life, Harry estimated that no-one had been in the room for several months, probably since school had started. There were still ingredients resting out on the tables, and some notes, although the cauldrons stood empty.
Harry wandered over to the cauldron that had the least dust on it and saw something that wasn't by any of the other cauldrons; sitting next to the pewter basin was a little stylized glass vial, holding some sort of grayish smoky substance. He uncorked it and poured the smoky liquid into the cauldron with a sizzle. It swirled around for a bit before settling into a rough pool, sending up a few tendrils that waved about in the air for a few seconds before falling again. Odd.
Harry glanced at the notes which sat on the desk. The contents of the notes were indecipherable, though; while they were written neatly in a striking style which seemed familiar to Harry, they were very complicated, and he had no idea what kind of potion they would make. Harry let his eyes bounce around the page, trying to find any ingredients he recognized, but saw none. Qurandel flower, augery tailfeather, mimbulus mimbletonia bile…
Harry frowned. He remembered that last one. Mimbulus mimbletonia bile… he didn't know what the mimbulus itself was, but they had used the bile in the last Potions class before the holidays. Professor Snape had said it was generally non-reactive and used to settle unstable potions, except when mixed with acromantula venom, when it formed a powerful acid.
Harry continued to glance through the notes, not really knowing what he was looking for, then found it. The last step in brewing the potion – add exactly 3 pints of acromantula venom.
Harry's eyes widened and he glanced back at the pewter cauldron he had thoughtlessly poured the vial of smoky potion into; the potion was gone and there was a large hole right through the cauldron and the table. He ducked down for a moment and saw the acid pooled on the floor and beginning to spread, reaching out with the tendrils…
Harry's eyes widened further when he realized whose hand had written the notes. He had seen their writing dozens of times, marking his homework. Always finding something wrong that he could've done better, but always pronouncing his work acceptable, that vaunted goal which so few reached.
Snape had brewed the acid.
Harry fled the room.