Seeing Snape stand in the Chamber of Secrets with his arms crossed was kind of surreal. Hermione still couldn't really believe he'd agreed to this. But Snape was adamant.

And oddly, it made a twisted sort of sense.

Professor Snape was her Head of House. As Head of Slytherin, it was Snape's responsibility to oversee the Slytherins and keep them in check. As a former Slytherin student himself, Snape knew that outright forbidding her from practicing her Dark spell would just result in her going behind his back to practice it anyway.

Turning her in to Dumbledore would violate the trust all of Slytherin House had in him. No one would ever trust him again, which would be objectively worse – if students didn't trust Snape to ask for help when they needed it, like she had, far more of them would fall prey to the Dark Arts than before. So Snape couldn't go to Dumbledore – or rather, he wouldn't go to Dumbledore, which had Hermione still slightly incredulous, but incredibly, incredibly grateful.

So the best course of action was for Snape to help her with the spell, keep her safe, and make sure she mastered it quickly, while observing to make sure she didn't fall prey to the lure of more Dark magic in the process.

It was like how her parents had offered to let Hermione try wine for the first time under their eye in their house, so she could experience what it was like to be drunk in a safe, controlled environment before she experienced it out in the wild. Hermione had never taken them up on it – after she'd left muggle school, it was clear it her future social life would look very different than previously envisioned – but it felt similar in intent to Snape's offer now.

If Snape wanted to come with her to make sure she wasn't going to accidentally burn herself up into ash until she mastered the spell, she wasn't about to object – and he would undoubtedly be immensely more helpful in offering protection from rogue Fiendfyre than Tom had been, whose strategy had been to run and hide in a sewer pipe.

Still. It was incredibly surreal to have a teacher semi-condoning her actions.

Snape. About to watch her cast Fiendfyre.

It was mad.

"Here?" Snape sniffed. "I smell… maybe something…"

"It burned up the dementor, but that was really all there was to burn," Hermione offered. "Which is why there's probably not much of a smell left?"

"A dementor?" Snape whirled around. "You got—"

"I got a boggart," Hermione said hurriedly. "Not a real dementor. Just a fake one to practice destroying."

Snape eyed the box she was holding.

"So I am to believe you have already destroyed a boggart with your Fiendfyre practice," he said, "and now you have another boggart to destroy as well?"

"Um," Hermione said. "Yes?"

Snape raised an eyebrow.

"Were it anyone else, I would question their sanity," he said. "But you are honest to a fault, Miss Granger. I fear to wonder just how you are obtaining these boggarts."

"Boggart farm," Hermione said promptly, setting the box down in the middle of the room. "Ready?"

"No," Snape said curtly. "Explain to me exactly what is about to happen."

"Err—okay. I'm going to flip the lid of the box, and the boggart will come out as a dementor," Hermione said, gesturing to the box. "Once it does, I'm going to cast Fiendfyre to destroy it."

"Try to cast Fiendfyre," Snape corrected.

"No, I've already done it, Hermione said, frowning. "That's how I felt the Dark allure."

Snape gave her a sharp look.

"I was under the impression you were trying to destroy things with fire, and you felt the joy of destroying things," he said.

"I mean, that's not inaccurate," Hermione hedged. "It was just with Fiendfyre, not normal fire."

Snape pinched the bridge of his nose.

"Miss Granger," he said. "What is the incantation to cast Fiendfyre?"

"Malignis Fiendfyre," Hermione said promptly, and Snape groaned.

"How did you learn that?" he demanded, and Hermione flinched.

"Erm," she said. "Around?"

Snape growled something vicious under his breath before straightening up, clearing his throat, and fixing her with a look.

"So I am legitimately to believe that you, a third year, have managed to cast and control this extremely advanced and Dark spell?" Snape asked, skepticism evident in his voice. "Miss Granger, fire by itself can be very intoxicating—"

"Ugh, just—look, I'll cast it, and then you can be the judge of whether or not it's real Fiendfyre, alright?" Hermione said, frustrated. "Ready? Go!"

Before Snape could get a word in, Hermione had gestured at the box, flipping the lid. A boggart-dementor emerged in a cloud of darkness, but her wand was snapping through the air, her magic touching the ember of execration smoldering in her soul as it reached for her fire elemental as well.

"Malignis Fiendfyre!"

Raging fire poured from her wand, this time as a giant serpent, and Hermione could feel her fury and hatred and frustration boiling out of her, cold control and power the only thing holding back the flames from destroying her and Snape as it had the box in the center of the room. The boggart-dementor had scarcely stood a chance in the face of the Fiendfyre serpent, and the box had disappeared in a wisp of ash in the wind.

The fire surged around the room, roaring and furious, but Hermione held onto the reins firmly, the cruel, dark sense of power and intoxication giving her the strength to control the wild hellfire. She glanced over at Snape, who was openly gaping at the serpent, his face a mix of astonishment and horror, and a dark sense of satisfaction curled inside of her, a warm, smirking feeling.

"Can you end it?" Snape asked. His voice was remarkably level, neutral, but the tension in his face and white-knuckled grip on his wand betrayed him "Can you stop it still?"

She jerked her wand up sharply, the roaring serpent curling in on itself with a vicious hiss as its flames vanished in midair, dissipating away into nothing. A heavy smell of ash and sulfur lingered in the air, and Hermione turned to Snape.

"See?" she said pointedly. "Fiendfyre."

This time it had been different, she mused to herself. It was as if finding the level of hatred necessary once had carved a path to it, making it easier to find now. The control came easier too, this time, now that she knew how to do it. She had to feel the hatred but not get lost in it, and she had to make sure her fire elemental was filtering her magic, too. Controlling the raging fire had been mildly terrifying the first time, in retrospect, when she hadn't controlled it fully from the start, but this time, she'd held the reins on the hellfire firmly, not dropping them even once.

It was kind of reassuring, too. Knowing she'd had such control from the start boded well for her future needs. And even as intoxicating as casting the spell was, just having Snape nearby to grab onto if she started to slip further toward the Dark Side helped her feel like she was less likely to fall over that edge.

Snape looked back at her, eyes unreadable even as they glittered.

"Fiendfyre," he finally agreed, his voice hoarse. "I suppose I should say well done, Miss Granger. That's an extremely advanced Dark spell you seem to have mastered. I have never seen such control from anyone without years of practice."

Hermione beamed under his dubious praise.

"Do I earn points for Slytherin, sir?" she asked, smiling and proud.

Snape snorted. "Don't press your luck."