Disclaimer: I don't have any claim on the Harry Potter franchise. I'm not going to rewrite that every chapter, so imagine the disclaimer is there in spirit.
No Defense Against the Dark Arts teacher had ever lasted more than a year at Hogwarts. Prue knew it, the current DADA teacher knew it, everyone was aware of the long line of incompetent or dangerous teachers hired and dismissed from the school as a matter of course. The only competent professor brave enough to test her luck against this curse, Mrs. Scamander, had taught non-consecutively for five years in ten, but this, Prue's first year, would be the last in the cycle. Mrs. Scamander's twin boys would be joining Hogwarts the next term, and Hogwarts would be left without for at least seven years.
Prue begged Mrs. Scamander to keep up teaching, citing horror stories some of the older students had told her of professors who let loose magical creatures to 'prepare' students, who misinformed kids and said that centaurs should be dealt with like garden gnomes, and who got into scandals with seventh years that no one would explain to Prue the details of. So Mrs. Scamander told Prue everything she knew about the curse. Prue had heard of it before of course, but only from students' gossip. She hadn't really believed it. After Mrs. Scamander had acknowledged it, Prue wrung out every bit of information she could from her teacher, and in the process learned more about the wizarding world's last war than she had learned all that year.
Before Mrs. Scamander would explain the curse, she insisted on teaching Prue a bit of history. Prue didn't mind. Mrs. Scamander was a war hero, close to the Harry Potter and knew more and was more candid than all of Prue's first-year histories. She spoke about Voldemort, whose name was really Tom Riddle. She knew everything he had done and everything he planned to do, and answered Prue's every question. She told Prue of his hatred for Albus Dumbledore (a great wizard, and yes, young Albus Severus's namesake) and how his wounded pride had led him to cursing the Dark Arts position. And eventually, after some more prodding from Prue, she confided what Harry Potter had done to stop him. Mrs. Scamander had a first-hand account for most of her stories, excepting Harry Potter's first year. Prue came back to her office every chance she got before the end of term to hear more. She lost the tenuous hold on the early friendships she had gained, but that only meant that she could spend more time talking to Mrs. Scamander and researching on her own.
At first she researched the recent war, but she was getting a more comprehensive knowledge from her Defense teacher than any text. She moved on to researching curse-breaking, a subject anyone who saw her studying told her was out of her league. Again, she got her most valuable knowledge from Mrs. Scamander.
"I don't understand why no one is doing anything," Prue said. She knew she was whining, but she was irritable after another late night studying. "I asked Mr. Flitwick about the cursed position, and he acted like a new teacher every year for fifty years was just a coincidence."
Mrs. Scamander had poured herself a cup of tea, but apparently she was dissatisfied with the result because she poured the cup's contents back in the pot and tried again. She said, "Adults are more susceptible to Gribblywinks than children. Mr. Flitwick believes what he told you is true."
"Gribblywinks?" Prue said, testing the phrase to see if she'd heard correctly. At her teacher's serene nod, she asked, "What are Gribblywinks?"
"Gribblywinks hide things for wizards, not that many wizards appreciate the favor. They can't help but hide themselves too, you see."
"If no one can see them, how do you know they exist?"
"I didn't say no one could see them, Prue, only that they hid themselves."
"Oh. Well, how can you see them?"
Her teacher took a sip of her tea, while pouring the rest of the pot in a plant by her desk. She said, "Have you ever heard of Threstrals, Prue?"
Prue thought about it, knowing that even though the question seemed random to Prue, her teacher expected a real answer. "I think I've seen the name before— in a list. Isn't it a kind of horse, like a Granian?"
"That's right, but Threstrals only look like they are related to Granians. They are a completely different type of magical creature." She finished her tea, then hummed at it and showed it to Prue.
Prue peered into the cup, even though she sometimes wished her teacher would get to the point faster. The tea leaves inside were grouped together in a recognizable image. "Is that a horse?"
"A Threstral." She corrected kindly, taking the cup back. "The reason you don't know much about Threstrals, is that wizards consider them a bad omen. Some even considered them spirits before the Ministry organized more fully and was able to document them."
Prue let her teacher clean up the tea things, but then prodded the conversation along. "Why were thestrals considered a bad omen?"
"Because thestrals were made by Death. They only eat dead creatures' flesh and can only be seen by those who have seen death."
"Oh. I can see why that would make people uncomfortable."
"It is not their fault, Prue. Thestrals are kind and intelligent. They pull the school carriages that many people call horseless. They serve wizards' needs but are hardly acknowledged."
"Like Gribblywinks," Prue said. She had learned that she had to make the connection herself, or the conversation would never get back on track.
"Yes, like Gribblywinks. They can't be seen either, unless you notice them before your magical core has fully developed."
"How do I notice them, then? I don't want to be like Flitwick."
"Professor Flitwick," Professor Scamander corrected.
Prue nodded, blushing.
"Gribblywinks love hidden things. They get very upset when something hidden is revealed, and for a moment flock around the hidden thing. Sometimes, a few of them get so upset that they forget to hide themselves. If your magical core is pliable enough, it will adjust to their presence, and once you know to look for them, you can find them."
"I've revealed disillusioned feathers in charms class before. I've never seen them."
"That's not so upsetting. It's the big things that get them riled up."
Prue considered that, then said, "How did you first see them?"
"I saw new magic uncovered often when I was young. It was four times before I noticed, and that was when Gribblywinks were at their most frantic."
"So I have to watch people make up new spells, or make up some of my own."
"Don't, Prue. There is too much that can go wrong if you don't know what you're doing. Magic can be dangerous, and you might uncover something that gets you killed."
Prue looked down from her teacher's uncharacteristically focused gaze, and said, "How am I going to see Gribblywinks, then?"
"Keep an eye out whenever something hidden is revealed," Mrs. Scamander said, wiggling her fingers by her head for emphasis. "It may take a while, but you're only eleven. You have time."
"I'm going to miss you next year, Professor Scamander. I don't think I'll learn as much from anyone as I have from you."
"This is your first year learning magic, so there was more for me to teach."
Prue tilted her head noncommittally. "Still… This curse should be broken."
"I would still be leaving if there were no curse. Lorcan and Lysander need to be taught Defense by someone other than their mother."
"And instead we're going to be taught by people who don't know what they're doing. Unexperienced teachers every single year." Riled by her own words, Prue said, "It can't go on."
The Professor smiled. "Voldemort was a very powerful wizard, Prue. It's safer to leave the curse until it loses power on its own."
"How long will that take?"
"Maybe a hundred years or so. Generally curse-lives are dependent on the power of the wizard and the intent they put into the spell. Voldemort was very powerful, but the curse on the position was probably only a passing action. I'll teach every other year until it's gone."
"You'll teach for a hundred years?" Prue said, raising her eyebrows.
"Wizards live longer than Muggles. Most can make it to two hundred if they try."
"That's silly."
"Magic doesn't often make much sense. Don't worry over it so much."
Prue was shooed out of the office. Mrs. Scamander wanted her to head to dinner, but she had too much on her mind to eat. She looked in the book about curse-breaking that she had begun bringing everywhere with her and read it over again.
Prue stole a book from Hogwarts. It wasn't really stealing, she told herself- she planned on bringing it back. Her thievery, not that it was stealing, was in the name of her continuing research on curse-breaking. She couldn't just put that on hold over the summer, not when she was actually starting to get a handle on the principles. Before she had left school, Prue had placed a curse on a plant and broken it without having to resort to the countercurse. Her small success had thrilled her, but breaking one of her own curses was only the first and simplest step.
To break a curse you had to be able see it. To see a curse you had to be able to see magic. Learning to see magic was like trying to see colors outside of the visible spectrum, but Prue did it. She taught herself to concentrate and wish and see flares of magic even when they weren't active spells like those used in duels. Although most magic appeared in wavering glimmers, her own familiar signature came through clear. She couldn't be satisfied with that. Every day she worked and learned and practiced, and every day the glimmers got a little steadier.
Her mother was a witch, so Prue briefly considered asking her for help. She threw away the idea almost immediately. Curse breaking was laughably out of the league of a soon-to-be second year, and Prue wouldn't enjoy looking silly when she told her mother what she was up to. Besides, her mother was Wandless, a witch officially integrated into muggle life and removed from magical society. Whatever advice she might be able to give Prue wasn't enough when she could no longer cast a curse herself.
When, halfway through vacation, Prue had decided she had gotten as far with theory as she could go, she went looking for something cursed. Sighting curses didn't require her to actually use magic. It was the breaking that would get her caught by the trace.
Prue lived close enough to Diagon Alley, over across the Muggle divide, that she could safely visit as if she were a Muggle walking to school. She gave her parents the excuse that she wanted to buy school supplies, then made her way to the Alley and spent her day trying to catch sight of the green haze that surrounded something cursed.
One witch had cursed her own hair. When Prue saw the halo of green around her temple and the moving zigzags that netted the strands of perfectly straight hair, she couldn't resist the opportunity given to her. A simple self-applied cosmetic curse wouldn't have any nasty backlash. It was the exact next step needed to practice. After following, studying, sighting, for two minutes, Prue flicked her wand at the woman's head. The hair immediately sprung in all directions in a curly poof, and the woman ducked into the nearest alley to reapply the curse.
Prue ran home and waited for the letter from the trace office to come, wondering what her punishment would be but giddy all the same. The letter never came. Prue concluded that her bit of magic was muffled by the magical activity of the alley. Afterwards, she went back every chance she got, when her parents would agree to take her or when they were out, whether they knew about her trip or whether they did not. As she attempted to break more curses, she grew more confident. She knew every page of her stolen, scratch that, borrowed book. She knew more about curses than was necessary in the life of an average witch. Still, she pushed herself into working on more complicated and stubborn curses. She had to improve in little increments because, when trying to break worse curses, she could expect worse backlash if she failed. The weekend before her birthday, Prue treated herself by exchanging her grudgingly earned allowance money at Gringotts and taking a look at their defensive Curses.
Somehow, a goblin caught her and she was banned from Gringotts for a hundred years. And she got a thorough talking to. Mrs. Scamander and Headmistress McGonagall also came to have a sit down with her parents, who grounded her for a hundred years.
As the Headmistress and her parents had their talk, Mrs. Scamander pulled Prue aside.
"I have to ask for the book back now, Prudence."
Prue gulped, and said, "The book?"
"The books at Hogwarts have enchantments on them that signal when a library book is taken out of the school. Madam Prince wanted me to get it from you right away, but I told her not to worry. You made me regret vouching for you, Prue. I thought you were responsible."
Prue flushed, and nodded. "I didn't know the goblins would get so angry."
"I suspect you've done more than just look at curses, Prue." She said. "You can't try magic you aren't ready for. I told you it was dangerous."
Prue looked down, and for the first time during her scoldings, her eyes started to sting. She looked up, trying to ignore how tight her throat was but unable to respond.
Mrs. Scamander said, "Get the book."
Prue hurried up the stairs to her room, finding the place where she'd left it easily. She had read the book a thousand times anyway. There was no reason she needed to keep it.
As Mrs. Scamander accepted the book from Prue, she said, "I'll take it back to Hogwarts myself and I won't tell anyone my suspicions, but you have to be more careful."
Prue nodded, but just as Mrs. Scamander was turning away, she said, "I should return it."
Her favorite teacher turned back to her.
Prue continued, "I took it, so I should return it. I'm sorry. I should have listened to you."
Mrs. Scamander considered her, then said, "Mrs. Prince is still at Hogwarts. Will you apologize to her as well?"
Prue nodded.
"If you come with me, I'll have to tell your parents about the book."
Prue winced, but said, "I know."
Her mother's face got even redder after Mrs. Scamander was done. She opened and closed her mouth a few times before settling on saying, "No wonder the goblins thought you were planning to rob them. I didn't raise you to be a thief, Prudence."
Her father pulled his head out of his hand and said, "Let her go. Maybe apologizing will keep her from being banned from the library for a hundred years too."
So Prue was side-along apparated to Hogsmede, a small village from which you could walk to Hogwarts. She was taken through Hogwarts' gates, after which she returned the book and apologized to Mrs. Prince with tears in her eyes.
As soon as Prue was alone in her room again, she stopped the waterworks, already planning her way back to Hogwarts.