Disclaimer: Only J.K. Rowling owns Harry Potter. Not me, sadly.
"The Boil-Cure Potion!" cried Professor Slughorn, his third chin wobbling dangerously. "Very useful to Madam Pomfrey up in the Hospital Wing, so consider today's lesson very important for the future!" At this he waved a plump finger at poor Robert Midgen, whose reddening face highlighted the unfortunate results of a Marauder prank. Petunia sniffed; Professor Slughorn's inability to become aware of anything negative about his favorite Marauders always grated on her logical sensibilities.
James Potter chose that moment to snigger. "Shame that there aren't any potions to cure greasy gits, eh Sirius?" Sirius Black guffawed, turning to toss a taunting look back at Severus.
The laughter drew Slughorn's attention; the man turned towards their direction with an indulgent expression. "Something to share with the class, boys?" he boomed.
Black offered his most charming smile at the Professor—which, Petunia had to admit with great reluctance—was a very effective one. "Nothing important, Professor," he said. "Just pondering on the strength of grease."
Slughorn smiled back, clearly confused but happy to appease the two charismatic boys. Potter and Black sniggered once more, watching in delight as Severus' face grew red with rage. Petunia watched with dissatisfaction as Lily, Severus' potion partner, grabbed his wrist and whispered frantically, obviously trying to clam him down. (Petunia thought the Marauders merited a good hex or two.) For the meantime, it worked; he settled with a nasty glare towards a still-giggling Pettigrew.
The class settled down as each student began preparing the required ingredients. Because Rachel refused to touch bugs, Petunia was responsible for stewing the horned slugs, while her friend deemed to crush snake fangs while keeping an eye on the nettles they needed to dry over an open flame.
"I have no idea how I can feel such disgust and pity at the same," said Rachel as she looked at Petunia dropping live slugs into the boiling cauldron water.
Petunia shrugged. "I imagine it's how we can eat beef or chicken comfortably but can't bring ourselves to kill the poor beasts ourselves," she said, stirring the slugs. She then used her wand to lower the flame. Rachel then brought over the dried nettle, dropping each strand every three clockwise stirs.
"What's next after the nettles?" asked Petunia.
"The book says to dump the snake fangs all at once after ten minutes of stirring, followed by the porcupines after we take the cauldron off the flames," recited Rachel without looking up from the potion.
Petunia shook her head in amusement. "Trust you to memorize the text," she said.
Rather than looking proud, Rachel looked a bit exasperated. "It's so that I don't completely fail the quizzes Professor Slughorn gives us," she said, referring to the weekly written exams preparing them for actual potion-brewing.
"That's really true," Petunia agreed. "Speaking of which, for next week's quiz, do we need stewed toads or stewed frogs for the potion?"
Before Rachel could reply, a new voice broke into their conversation. "Trust Ravenclaws to talk about schoolwork above all things," said Sirius Black with a smirk.
Petunia faced him with slitted eyes. "What do you want, Black?" she sneered. Added on to the fact that only he challenged her in DADA twice a week, Petunia disliked his arrogant nature. Perhaps, she told herself wryly, because she herself also tended to be proud. Didn't a person dislike their own characteristic traits in others?
Sirius raised his hands, trying to show his defenseless state. "Nothing much, Evans," he said with an appeasing smile. "Just asking to see if you could spare some porcupine quills. James and I are out, you see."
"Why don't you use the Potions stores?" asked Rachel sensibly, trying to defuse the tension. "I'm sure there are bunches there."
"Ah Moon, you'd think, being a Pureblood, you'd know that store ingredients aren't fresh," Sirius replied.
Rachel conceded the point. "Maybe so," she said.
Petunia quickly grabbed some quills and thrust them in his hands. "Take them then," she said. "Will you go away now?"
Sirius winced as a few poked his hands. "Thanks, Evans," he said, before walking away. Petunia watched him for a few seconds, Lily and Severus catching her attention in the way. She could see that as always, their potion seemed to be a couple steps ahead of her own, already turning thick and creamy.
"I don't really see why you hate him so much, Petunia," said Rachel, trying to pick up their potion off the flames.
"Let me help," said Petunia, grabbing one end of the surprisingly heavy cauldron. She continued, "And I know it's not completely logical to hate him, as he hasn't been rude to me personally, but I just do. He's so mean to Severus!"
Rachel opened her mouth to argue back, but at that moment something exploded on the other side of the room, causing mild chaos. Petunia swerved around—it was Severus' cauldron!
"That can't be," said Rachel. "Severus never messes up the potion."
Petunia, however, was distracted by the sight of Lily lying on the floor. "Lily!" she shrieked, and sprinted to a stop beside her unconscious sister.
Severus was crouched beside her as well, looking bewildered and panicked. "I didn't—I don't understand—it was fine—" he babbled.
Professor Slughorn quickly came over to examine Lily. "Just unconscious, fortunately," he said, casting a spell to lift her into the air. "I'll take Ms. Evans up to the Infirmary. For now, consider the class dismissed!" As the other students began packing up their materials, the Professor stopped to peer at the cauldron contents. "Porcupine quills added while on the fire?" he mused aloud, surprised. He turned to Severus. "Quite unlike you, my lad," he said. "But accidents happen to the best of us, I daresay." He began shuffling off, unaware of Severus' suddenly furious expression.
"I made sure to keep the quills away," he said, grappling for his wand inside of his robes. "They're extremely hazardous, of course I wouldn't put her in danger—!"
Petunia also realized who the culprits were, a chill settling down on her features. "Black," she snarled, and even Severus stopped to stare at Petunia's glacier expression.
Rachel darted to her side, somehow understanding what would happen. "I'll follow your sister to the Infirmary," she promised, and ran to keep up with Slughorn.
The Marauders were frozen at the front of the classroom, staring at the space where Lily had lain.
"We're so incredibly sorry," came forward Remus, his hazel eyes wide. "We didn't—I didn't," he stammered.
Petunia strode forward, "Move, Lupin," she said, her voice deadly calm. Severus came to stand behind her, silently watching her back.
"Petunia, that wasn't—," began James, but he was cut off by Petunia rushing forward towards Sirius.
"I know what you did, Black, and I'm furious," she said softly. "Lucky for you, I know that the explosion couldn't have been fatal. But if you try to hurt my friends ever again—!" her voice rose to a shriek, and in a moment of pure frustration, Petunia kicked Sirius between the legs. He toppled over with a cry of pain, oblivious to the panicked Marauders fluttering around him. Meanwhile, Petunia sniffed and rushed out.
Severus paused to glare at the Marauders, disdainfully glancing at the whimpering Sirius. "I let it go when it was just me," he said said. "But now that Petunia will be helping me, you'd better watch out." With that, he followed after the Ravenclaw with robes a billow.
Even though Petunia logically knew that Lily was alright, she couldn't help feeling guilty as she watched her sister sleeping against the pristine Infirmary sheets. After all, it had been Petunia herself who had handed Black the porcupine quills!
"It's not your fault, Petunia," said Rachel, correctly guessing at her thoughts. Her next words, however, were unexpected. "If anything, it's mine!"
Petunia looked at her friend in astonishment, shocked out of her guilt. "What do you mean? I was the one who gave Black the quills."
Rachel sighed. "Well yes, but if I had just made Sirius use the quills from the Potions stores, Lily wouldn't have gotten hurt."
"That's stupid," Severus butt in. "It's the Marauders' fault. Black would've gotten the quills from somewhere either way."
Petunia looked at Severus. "I want to get them back, Severus," she said furiously. "It's time to take them down a notch."
"I agree," said Severus. "I have to admit that I have a lot of knowledge on hexes, Petunia. If we use those—"
"No," broke in Petunia, shaking her head. "We need to make a point, Severus. I want to show them how cruel and humiliating their so-called pranks can be. I want them to feel just how Robert Midgen felt with his face covered in boils, and Alice Macmillan with canaries nesting in her hair, and you over your looks, and Lily! No." She shook her head again.
"I don't know how I feel about doing the same things the Marauders do," said Rachel with a worried frown.
"No, I agree with Petunia. It's also a very Slytherin-ish plan," said Severus with an approving nod. Seeing Rachel's still-anxious expression, he relented a little. "Of course, you shouldn't feel obligated to be a part of this campaign," he said. "I wouldn't blame you. We'll be doing things that wouldn't exactly be approved of."
Petunia gave Rachel a nod. "You can go ahead, Rachel," she said. "Severus and I can discuss things on our own."
Although Rachel still looked apprehensive, her face relaxed at the thought of staying out of the surely coming chaos. Giving her friends one last glance, she slipped out of the Infirmary. Now alone with the sleeping Lily, Petunia and Severus put their heads together to plan their newfound vendetta against the Marauders. And that was how the Ravenclaw and the Slytherin found a common ground against the Gryffindors.
A/N: Thanks for all the reviews and the new followers/favorites! I'm finally back in college, and the work is seriously piling up, which is why this update is so late. It's a lot shorter than I originally planned on it being, but I wrapped it up so that I could release it faster. Please excuse any mistakes, and hope you all enjoy!