Snape was putting the finishing touches on the first stage of the Quest for the Quidditch Key when the door between the west corridor and the landing rattled. It was locked, of course, and so he ignored it. Perhaps a flaming sword … that should be appropriately terrifying and prevent them from thinking of outright combat …

"Alohomora!" Even through the door, Hermione Granger's voice was distinctive. The lock yielded to her spell.

The bolt that Snape had shot home as an added precaution did not. Now, should it appear half-way up the corridor? Or closer to the door?

"Bombarda!"

That did for the bolt.

Snape turned to see Granger silhouetted in the doorway, the door flat on the floor and smoking slightly. "Subtle."

She stomped inside, lifted the door with a wave of her wand and slammed it back into place. "Fiona Firewater needs to be taken down a peg or two."

He narrowed his eyes. "Is this another of those conversations where you have had the first five minutes of it without me?"

Granger glared at him. "Seventh year. Slytherin. Hates me."

Snape shrugged. "Have you tried hating her back?"

"Yes, because that will make everything better," Granger snapped. "I'll give her justification for her grudge, that will resolve the situation in no time."

"Don't be sarcastic," Snape said. His lip curled in a sneer. "You don't have a talent for it."

"I'm not being sarcastic, I'm bloody furious! She tried to hex a student in class today and gave me attitude over taking her wand."

Snape raised his eyebrows. "I presume you gave her detention?"

"Of course I did, along with an essay on the responsible use of magic and the need for restraint."

"Manually cleaning the Potions classroom would be more effective."

"As a punishment, maybe, but not to teach her what she really needs to know, which is to stop being such a bitch." Granger threw up her hands. "Honestly, I have no idea how she made it this far without someone teaching her a lesson. I mean, I know Draco was given far too much rope in our day, but there was a war on. The educational standards here are abysmal!"

"Says the Professor planning to entangle her students in an invented quest for an imaginary magical object."

She levelled one forefinger at him. "Don't change the subject! This school has a responsibility —"

"Which. It. Meets," Snape bit out. "This is not a local comprehensive, Granger, and the students here are capable of rather more mischief than pushing each other over in the playground. Instilling a few principles of moral behaviour is a bonus when one's greatest concern is making sure none of our alumni accidentally level the centre of London in a fit of pique. If your student has reached her N.E. , she has clearly learnt what she needs to learn."

"You can't turn out students who think they can hex someone for insulting them!"

"Again, Granger, you make assumptions. Hogwarts can't turn out students who can't cast charms reliably, brew potions accurately, and who hex people accidentally. If they do so deliberately, there are Aurors for that."

"And meanwhile, Fiona carries on regardless?"

Snape shrugged, careful to turn his wrists a little to convey just how absolute his indifference was. "I believe the Muggle term is 'character building'. At least for her classmates. Now. Stand back, and observe."

He'd spent several hours on the illusion charm, and when the ghostly figure with its flaming sword came roaring down the corridor, Granger gave a gratifying squeak of alarm and raised her wand.

Snape allowed himself a smile of satisfaction and banished the illusion with a flick of his own wand.

"Why —" Granger started to say, cleared her throat, and tried again. "Why is it Gandalf?"

Snape frowned at her. "If this is your way of inducing me to ask what a 'gandalf' is …"

"He's a who," Granger said quickly. "A character. In a book. And a film. Who looks very much like that."

"I was aiming for 'generic wizard'," Snape said.

"Clearly, so was Peter Jackson," Granger said. "But they might have seen the film, so perhaps you could change it? Make it a bit less, um. Beardy. And younger? Maybe female, even." She cleared her throat. "What does it do? Besides rush and bellow?"

"A small fear charm, if they are foolish enough to stand their ground long enough for it to get close to them."

"And how are they supposed to get past it?"

"Quietly." Snape sent a beam of light from his wand to illuminate the other end of the corridor, where the model for the ghost stood — one of the innumerable statues that filled the halls and rooms of Hogwarts. Above it was his own addition: Woe betide who disturbs my sleep. He frowned, considering. If I alter the apparition illusion as Granger suggests, I will have to alter the statue's appearance as well.

"So it will be sound activated?" Granger said, proving that she had not lost the ability to state the blindingly obvious. "That's why you want the Hungarian Hiccoughing Gas."

"I recall from your lesson plan that they are due to study the Solution to Hiccoughs this month."

Granger nodded. "In fact, that was the lesson the Boggart interrupted. So this challenge will test … courage, of course, because they'll have to return having been chased out once. And brewing."

Snape inclined his head. "That will rely on Rowland's expertise. Longbottom tells me Aitkins aspires to heroics, so this particular trial is suited to him, as well." He paused. "Let us hope that they do not resort to another Boggart to acquire the ingredients."

Granger gave a wry smile. "I'll think of a way they can nab them without such extreme measures. How much time do I have?"

"Sufficient. I intend to insert a small reference to the Key in one of the Library books. It will take them time to uncover it, and decide they really want to find it."

Granger chuckled. "Don't let Irma Pince catch you. What else did Neville say?"

"That it would be fruitless to try and dissuade you from this ill-conceived enterprise," Snape said. "That Wilkins aspires to become a Beater. Both things I already knew."

"So what test will Maisie have to overcome? Something on a broom?"

"Yes, because encouraging students to fly indoors in confined spaces is so extraordinarily safe."

Granger only laughed, further confirmation that Snape was losing his edge.

"What, then?"

"Come." He led the way to the disused classroom at the end of the corridor. Granger gasped as she stepped through the door, which was gratifying — Snape had spent several hours on the Extension charms and other spells that had transformed it from a dusty room cluttered with abandoned desks to its current satisfyingly imposing form.

Granger walked slowly to the centre of the huge space, head back as she scanned the ceiling. Anticipating yet another attempt to break her own neck by tripping on her robe, Snape fingered his wand, but she reached the middle of the room without mishap. "What happens next?"

"Surely a puzzle designed for an eleven-year-old mind is not too complex for your own?"

She turned slowly in place, and he saw her face brighten. "Aha! Levers. On opposite sides of the room, clever. At least two of them will have to get through the corridor to be able to beat this."

"Three," Snape corrected. He crossed to the closest lever, and gestured to the other. "If you would?"

"On three," Granger said cheerfully, taking hold of the other lever. "One, two, three!" Stone rumbled overhead, and Granger tilted her head back again. "What was — oh, I see." She gazed up at the alcove that had opened far overhead and the small lever inside it, forehead wrinkled. "I thought you said they wouldn't have to fly."

"They won't," Snape said. "Indeed, when I've finished the charms on this room, they won't be able to. Come on, Granger. What do Beaters do?"

"They hit the Bludgers —" she began automatically, and then her mouth opened and stayed that way for several seconds before she shut it with a snap. "That's an awfully long way up."

"I do apologise," Snape said silkily. "I was under the impression that you wanted this to be challenging. Allow me a few moments, and I will lower the target to knee-height. Would you like me to make sure the outer corridor is guarded by kittens, as well?"

That brought a flush to her cheeks, he was pleased to see. "Challenging doesn't mean impossible."

"If you had spent more of your school years watching Quidditch for the game, and less time looking for teachers to incinerate, you would know that any decent Beater could easily hit an object that far."

"That was only once," Hermione said tightly. "I only did that once."

"Once was more than enough."

She cleared her throat. "Anyway. What happens when they manage to hit the lever? The Quidditch Key drops on their heads?"

"A disembodied voice," Snape said, with satisfaction. "Conveying a message which they must decipher, to locate the monster they must confront to finally gain the Key."

Granger gave him a sideways look. "I'm beginning to feel you're enjoying this."

He gave her his most haughty look. "Nonsense. This ridiculous twaddle is beneath me, or any other witch or wizard with sufficient skills to seek employment more advanced than entertaining at children's parties. I merely wish to make sure you don't endanger your students by attempting it yourself."

Her lips twitched. "You're putting a lot of thought and effort into something you don't enjoy."

"Granger, the purpose of this is to keep your troublesome troika occupied and out of trouble for the rest of the year. That will hardly be achieved without a sufficient number of steps to be completed, each with their own inbuilt delays. Deciphering the message will preoccupy them for several weeks."

"What's the message, then? And what's the monster?"

Snape paused. "The message is … pending."

"You mean you haven't worked it out yet?" Hermione asked.

He drew himself up to his full height. "Do excuse me, Professor Granger, I was —" He stopped, realising she was laughing.

"This is amazing," she said, turning around again to gaze at the cavernous space. "It must have taken you all day. I can't even see the seams on the extension charms!" She paused, and then turned to look at him, a frown wrinkling her forehead. "It wasn't too much, was it? You didn't tire yourself?"

He scowled at her. "Granger …"

She put her hands on her hips. "Don't glare at me! I appreciate the help, but it would be bloody silly for you to speed up the curse just for this!"

"I assure you," Snape said icily, "these parlour tricks hardly taxed my strength."

"Show me your arm," Granger demanded.

Snape drew his arm toward his chest, realised he was doing it, and stood still. "Unnecessary."

"Don't be an idiot," Granger snapped. "It's all data. It got worse after your Legilimency, didn't it? Then it stopped. If it's worse now, that means it is to do with —"

"Any number of things," Snape said. "My assailant might have gained access to his conduit again. The erratic effect of the potion you devised may have manifested itself once more." He raised an eyebrow. "I'm surprised, Professor Granger. I would have expected your studies to have cured your lamentable tendency to allow your theories to advance ahead of your facts."

"Yes, well, unfortunately, we don't have a control group, do we," Granger said tightly. Her wand was in her hand. "Are you going to unbutton your sleeve, or do I cut it open?"

Snape narrowed his eyes. Granger gave every impression of being entirely serious. Of course, given how she usually dresses, she would have no idea what decent tailoring actually costs. Not that she had any real chance of an offensive spell hitting home, but who knew what damage it might do to the spells he'd spent … longer than he cared to admit … creating?

Scowling at her, he unbuttoned the cuff of his coat, then his shirt, and pushed his sleeve up. He had no need to see the withered flesh again to know it was there, and kept his gaze fixed on the wall.

Until Granger breathed "Nimue's new knickers," and grabbed his wrist. Startled, he looked down as he pulled away —

And froze. Not possible.

"I would have said there was less than an inch to your elbow, the other night," Granger said. "Now …" Careful not to touch him, she measured off the distance from the crook of his elbow to the upper edge of the grey, dead skin of the curse.

All four of her fingers. Twice.

She let go of his wrist and looked up at him, eyes wide. "Did you do something? A new potion? A spell?"

"No." Snape tried to tear his gaze from the miraculously shrunken oval of cursed flesh, and failed. "No, nothing except to continue to take the potion you devised."

"We devised," Granger corrected with a small smile. "And you've been working all day, so the flare-up wasn't fatigue, was it? And if the person doing this did their worst the other day, well, it wasn't very effective, was it?"

"One more conclusion," Snape said. "Your misgivings about the potion were unnecessary. It clearly continues to work."

Her smile grew, until it was so brilliant it could only be described as beaming. Or ridiculous.

"There is no need to get ahead of yourself," he said as repressively as he could.

It failed to put a dent in her happiness. "I'm not," she said simply. "The only way to finish it for good is to find out who's doing it, I know that. But now we have enough time." Her eyes glistened, and Snape realised with alarm she was about to start leaking tears again.

"I will need all the time I can get if I'm to correct some of your absurd ideas about coddling students," he said acidly.

Hermione laughed, and sniffed, and turned away for a moment. When she turned back Snape was relieved to see she had composed herself. "So," she said. "The final clue, which is pending — what does it need to lead to?"

Snape told her, and the huge room echoed with Hermione Granger's laugher.