"Stuff," Snape said with acid contempt, and Hermione laughed, partly at the incongruity of hearing Severus Snape at his most Snape-ish while the man himself remained invisible. She crossed to the door and bolted it.

When she turned, he had removed the cloak. "You should have made the boy copy those reports, not just read them."

"That would take more detentions than I'm prepared to supervise," Hermione said. She picked up the box of records and carried it to her desk.

Snape followed her. "I'm … surprised at your lack of dedication."

"No, you're disapproving of my lack of disciplinary enthusiasm." Hermione picked up the report on her own misadventure that she'd removed before letting Colin loose on the files.

Snape plucked it from her hand. "As I said." He studied the parchment, and the corner of his mouth turned up slightly. "Professor Granger, if I'd know you would treasure this so, I would have made sure you received a copy on graduation."

"I'm not treasuring it," Hermione said. "I didn't think letting a student read it would be particularly conducive to the lesson I wanted to impart."

A spark of what might have been humour lit his dark eyes. "Knowing their teacher got up to far worse than infusing broom handle polish in her own time as a student."

"Exactly," Hermione said. Honesty forced her to add, "That, and knowing they'd be picturing me with ears and tail for the next few months."

"Minerva is the only teacher I've known to be able to carry that off without a loss of dignity." It was definitely humour in his eyes, and he was almost smiling. He glanced down at the parchment. "Miss Granger has undertaken —"

"I don't need to hear it," Hermione interrupted, feeling her cheeks grow hot. "I can imagine what you thought —"

"A most ambitious illicit project, to wit, brewing Polyjuice Potion," Snape continued smoothly, as if she hadn't spoken. "This advanced Potion has defeated many a N.E.W.T student. Granger's unfortunate current condition is undoubtedly caused by the use of cat hair instead of human hair, an error I am certain she will not make again."

"Yes, alright," Hermione said.

"The fact that the Polyjuice Potion had any effect at all," Snape continued, "with the addition of animal hair, is testament to impeccable brewing on Granger's part, particularly noteworthy given the clandestine nature and no-doubt suboptimal facilities. While the theft of supplies from the school storage-room deserves severe punishment, it is the inescapable conclusion that the theft itself was carried out by Potter, and that Granger's participation was due to his bad influence alone. Therefore, given the length of time it will take to return Granger to her normal appearance, I recommend no further disciplinary action."

Her gaze flicked up from the page to meet hers, and his eyebrow lifted slightly. "As I said. It was remiss of me not to make sure you received a copy on your graduation."

"It was actually me," Hermione said, smiling a little. "Who stole the ingredients. And who hatched the whole plan."

Snape's eyebrow raised a little more. "You have hidden depths. I suppose I should have realised. It would have been most unlike Potter and Weasley to listen in class."

"Harry did throw the firework," Hermione said.

"A shame I can no longer have him expelled," Snape said. He held out the report. "For your files, Professor Granger."

She took it, unable to resist a quick glance to see if he'd in truth read it accurately. Ambitious .. impeccable brewing … suboptimal facilities … all in Snape's familiar angular writing. "I think this is the nicest thing you've ever given me."

"The fate of the teacher," Snape said, scowling at her. "To have six years of marking your excessively long essays comprehensively disregarded."

Hermione laughed, thinking of some of the efforts of her own students, especially the Ravenclaws. "I won't apologise for the Polyjuice Potion," she said, "because that was a really good idea. I will, however, apologise for every essay that was so much as a line over the requested length."

"All of them, then," Snape said. Despite his frown, Hermione was certain she could still see a hint of humour in his expression. "The apology is unnecessary, Professor Granger. Your work was less painful to mark than most."

It was almost a compliment. By Severus Snape's standards, it probably is a compliment. "Thank you," Hermione said.

He sketched the slightest inclination toward a bow, little more than a movement of his hand and the inclination of his head, and Hermione was suddenly acutely aware that if they failed to find the cause of the Dark curse Snape bore on his arm, she would lose more than the chance to make right her failure of five years ago. She would lose the pleasant surprise of puzzling through an insult to find the compliment wrapped inside it; she would lose being ambushed by amusement when Snape took his acid contempt for the entire world one minute shade into self-parody; she would lose the enjoyment of intellectual fencing with a mind as sharp and nimble as her own.

"Granger?" Snape asked, and Hermione realised she was staring at him in silence.

"Sorry," she said, forcing herself to smile. "Just thinking about the Quidditch Key. But I've got to dash, I'm sorry — I promised Harry, I'd, uh — do something."

"By all means," Snape said, and the humour, the hint of camaraderie, was gone from his voice. "You mustn't keep Professor Potter waiting."

Hermione felt oddly like weeping as she hurried upstairs to the Room of Requirement.

She was the last to arrive, slipping into the empty chair with a muttered apology.

I was just saying that we need to regroup," Harry said. "Let's run through what we know. Hermione?"

She sighed. "I'm afraid I don't have anything helpful to say. I've been through the whole list of Death Eaters recorded as killed at the Battle of Hogwarts and every single one was witnessed. No-one's unaccounted for."

Harry nodded. "And I heard back from Kingsley this afternoon," he said. "They're closing the investigation into my 'anonymous tip'. They're absolutely positive that no-one who ever took the Dark Mark escaped the net. Which means we can be sure that it's not a Death Eater actually casting the curse," Harry said.

The rest of them sighed or groaned, except for Luna, who sat regarding Harry mild interest.

"I'm sorry, everybody, but it isn't. Not a secret one, not one everyone thinks is dead. There's no Death Eater unaccounted for."

"It might be time to call in the Ministry," Ron said.

"No!" Hermione jumped to her feet.

"Hermione," Ron said reasonably. "You know what this means. It has to be someone with access to the Death Eaters in Azkaban. Kingsley has to know."

"And what if they still can't find out who it is?" Hermione cried. "Do you want Professor Snape to spend what time he has left on trial?"

"Do you want to keep secret the fact that one of the Aurors assigned to Azkaban is an active practitioner of the Dark Arts?" Ron shot back. "Because apart from the fact that it would be the end of my brilliant career when it came out, keeping dark wizards secret is about as clever as going for a midnight swim with the Giant Squid."

Luna frowned. "I don't think that's quite right, Ron," she said. "Because swimming in the Black Lake at night is actually quite fun, and —"

"Anyway," Harry said. "I agree with Ron. It would be one thing if we knew who it was, and could sort of arrange to find out some other way."

"But we do know who it is," Luna said in mild surprise. "Don't we?"

There was a small silence, and then Ginny said with calm patience, "You might know who it is, Luna. But the rest of us have no idea."

"Oh, that's right, I haven't shown you Daddy's pictures," Luna said. She produced the envelope she'd received in the morning mail from her robe. "Here."

She handed it to Harry, who opened it and took out five photographs. "Professor Snape," he said, studying the first one and then passing it to Neville. "So is this — and this —" He leafed through the others rapidly. "Luna, it's five copies of the same photograph. Of Professor Snape watching Quidditch."

"No, it isn't," Luna said patiently. "When people take photographs for newspapers they take several, all in a row, to make sure they get a good one. I saw that —" She pointed to the photograph Neville was now handing to Ginny, "on the front page of The Prophet for a story about Professor Snape. The story is rubbish, of course, but I wondered about the photograph, so I owled Daddy and asked him if he could find the photographer and get copies of all the pictures she took that day." She smiled at them all. "And he did."

"Right, well," Harry said, "I'm afraid I still don't have a clue who's cursed Professor Snape and these photographs don't tell me anything, so you'll have to explain."

Luna sighed. "Hand them here, then," she said. Once all the photographs were in her hand, she tapped them with her wand. "Commeditor Projectura!"

A thin stream of blue light rose from the photographs toward the point of her wand. Luna turned a little and directed her wand at the blank wall. Another beam of light shone out from it, and on the wall —

"Blimey, Luna, you've invented wizarding movies!" Harry said.

"It was Professor Burbage who gave me the idea," Luna said. "In class? She talked about how Muggles made pictures move by taking lots of them and running through them very fast. When I saw her in the picture, it just popped into my head."

"In the picture?" Neville asked, craning to see.

"There." Lune nodded towards the wall that was now doubling as a screen. "Beside Professor Snape."

Hermione peered at the picture. It had been taken on a cold day, and the person sitting next to Snape was so thoroughly wrapped in cloak and muffler Hermione couldn't even be sure it was a witch, let alone which witch. Snape, on the other hand, was dressed as he usually did. Either his warming charms work better than mine, or, more likely, he'd rather be cold than undignified.

The image jumped suddenly. "Oops, sorry," Luna said. "They've gotten shuffled." She rearranged the photographs in her left hand. "There. I'll go back to the beginning."

"Yes, thank you, but Luna, what exactly are we looking at?" Hermione asked.

"Just watch," Luna said serenely.

Hermione turned her attention back to the images. Professor Snape, looking so much younger than she'd ever seen him that the picture had to date from his early years teaching, stared away from the photographer, intent on the game. The rugged-up person beside him leaned sideways a little, nudging his shoulder with their own. Snape turned, said something —

And the person beside him doubled up with laughter. As she straightened, her muffler slipped down, and Hermione instantly recognised her as a much-younger Charity Burbage, nose red with cold. Still laughing, she shook her head and replied to Snape, trying to adjust her scarf with mittened hands. He turned to look down at her as he answered, and then —

"Bloody hell," Ron said, as Snape-on-screen deftly adjusted Charity's scarf to warp her warmly once again. "Looks like he got over your mum a lot faster than anyone thought, Harry."

"Oh, I don't think they were lovers," Luna said as the images reverted back to the beginning and began to play again. "He's very careful to only touch her scarf."

"Madam Hooch — Rolanda, I mean, she talked as if they were friends," Ginny said. "Professor Snape and Professor Burbage."

"That's what I think too," Luna said. On the screen, Charity Burbage burst out laughing again. "Friends for a long time, because these were taken in 1985."

Hermione watched as Professor Snape again drew up Charity's scarf so it protected her cold-reddened nose. "Well, that's —" mind-boggling "interesting, but I don't understand how it tells us who cast the curse."

"July," Harry said abruptly.

"Yes, exactly," Luna said with a smile. She lowered her wand and the moving pictures flickered out.

"I'm glad you two have worked it out," Neville said, "but I'm going to need a little more to go on."

"Professor Burbage was murdered by Tom Riddle in July," Harry explained. "July, 1997. Professor Snape was there."

"He gave you that memory?" Ginny sounded nauseated.

Harry shook his head. "I've seen the list the Ministry got from the Malfoys. Point is, if they were friends, Charity and Professor Snape, people who knew her probably knew that, right? And while it's bloody obvious there wasn't anything he could do to stop Voldemort killing her, it might not look that way to everyone."

"Hold on," Hermione said, remembering something she'd read in her research for updating Hogwarts: A History. She scrabbled in her bag until her fingers closed on her notebook. Dragging it out, she flicked pages. "Charity Burbage, born January 1956, started at Hogwarts in 1967, Hufflepuff. Graduated 1974, spent two years as a student at the Guildhall School of Music and Drama and then read Fine Art at Oxford." Ron circled his finger in a 'get on with it' gesture and Hermione glared at him. "First hired to teach Muggle Studies at Hogwarts in 1982, left the position in 1987. Returned in 1993. That's when we knew her." Ron opened his mouth and Hermione sighed. "I'm getting to it, Ron! Died, July 1997. Survived by her sister, Patience Monkshod nee Burbage, and her nephew —"

"Matthew Monkshod," Neville said, and Hermione nodded. "Second year, Slytherin House."

"Merlin's meaty member!" Ron said. "A relative of Charity Burbage sorted into Slytherin? That Hat has lost it."

"That's not the point, Ron!" Hermione said impatiently.

"I know it's not the point, alright? The point is that Charity Burbage's nephew has spent the last year in the dungeons and is as likely a person as anyone to see Snape —"

"Professor Snape," Harry corrected.

"Severus, because I'm a bloody Professor myself now. To see Severus flitting about, and to go home and tell his mum that the man who sat there and watched her sister die is alive and well."

"That is the point, yes," Hermione said.

Ron grinned at her. "Always the tone of surprise."

"That still doesn't get us past the Death Eater problem," Ginny said. "I mean, if it is Charity's sister, how's she doing it?"

"Is she even a witch?" Harry asked.

Hermione shrugged. "I don't know, but it would be easy to find out. But the point is, whether she's a witch or not, she's obviously aware of the wizarding world because of her sister, and her son. Someone could be helping her, someone at Azkaban. Someone must be, unless she's one of the Aurors at Azkaban herself."

"That takes us back to someone in the Aurors doing Dark Magic," Harry said. "We've got to report it."

"But you said, if we could work out who it was, we could discover them some other way," Hermione pointed out. "Now we have a clue who it is."

"But it's just a clue, Hermione." Harry raked his fingers through his hair. "If it's Professor Burbage's sister, then finding out which Aurors she knows well enough to ask for a favour, a favour this big, that's a huge operation. It's not something we can do between us, even if we weren't trying to fit it in between teaching."

"We could —"

"Hermione," Ron said firmly. "There's no way we could pull it off between us. You don't know —"

"Because I'm not an Auror?"

"Yes, because you're not an Auror," Harry said. "It's not — Hermione, I'm sorry, but it's not like it was at school. It takes loads of people, working together, around the clock watches —"

Hermione found herself on her feet. "You just don't —"

Harry stood as well, facing her. "It's just not as simple now as it was when we were bloody twelve, is it?"

"No!" Hermione put her hands on his chest and pushed, hard enough to send him backwards a step. "Back then we all did whatever you decided we ought to! It's not that simple now, not nearly!"

"I think —" Luna said.

"Calm down, Hermione," Ron said.

"Don't you dare!" Hermione turned to face him. "Don't you dare tell me to calm down, Ron Weasley! I'm not the one who threw a tantrum in the middle of —"

"Enough!" Harry bellowed. He'd developed quite the authoritative roar in his years as an Auror, and Hermione and Ron both fell silent. "Enough, both of you," he went on in a more moderate tone. "Ron and I aren't trying to boss you around for the sake of it, Hermione. We've been part of operations like the one that's needed here, watching witches and wizards suspected of something. Even if all six of us dropped everything and devoted all our time to it, we wouldn't have enough people to be sure we'd get a result. And we don't have any way to monitor her Floo, or read her mail, but the Ministry can and will do that."

"I think that —" Luna said.

Hermione put her hands on her hips. "You do realise that Professor Snape would rather die than have the Ministry, or anyone else, know he's alive?"

"It's not up to him, not any more." Harry took off his glasses and pinched the bridge of his nose. "I really should have told Kingsley that it was at least a possibility right at the beginning. I just didn't want to believe it could be true." He put his glasses back on and shrugged. "An Auror, a colleague, one of us, using dark magic? It should be impossible."

"It's not like they've gone full Death Eater, though, is it?" Neville said. "I mean, they think they're getting at a Death Eater, don't they? If they're helping Professor Burbage's sister."

Harry shook his head. "It's not like that, though. Casting a killing curse — it does something to you. You know how much you have to mean magic. You can't cast Expelliarmus properly unless you really want to disarm someone. That's why the Dark Arts are dangerous — because you have to reach into your own dark places to use them, and you have to nurture that darkness and make it stronger to use them effectively."

"And a killing curse," Ron said, "one strong enough that even Snape — alright Harry, Professor Snape — can't stop it, that's well bloody along that road."

"Oh." Hermione sat down again, twisting her fingers together. "And someone like that, in Azkaban …"

Ron nodded "That's it. They might be telling themselves that they're doing it for all the right reasons, but just trying to do it would change a person. Pulling it off … let's just say I don't want that kind of person in charge of making sure Voldemort's loyal servants don't get loose."

"Listen to me!" Luna said, in what was, for Luna, almost a shout. "Why don't you just ask Patience Monkshod?"

"That's bloody brilliant, Luna," Ron said.

"She won't tell us —" Hermione objected.

Ron grinned at her. "She won't need to. Hermione, think. Are we wizards, or what?"

.

.

.

Author's Note: I've made up certain details about Charity Burbage's past and private life, including the date of her birth, her Hogwarts House, the fact that she was at Hogwarts as a teacher in the 1980s, and her family.