If he was being entirely honest with himself, Severus Snape, former Potions Professor at Hogwarts and current … current whatever he was, wasn't entirely sure what had drawn him to the Potions classroom today.

But then, when was the last time I was entirely honest with anyone? So why break the habit of a lifetime? He'd dressed once again in the deep, unrelieved black that had been armour and disguise for two decades and shrugged into the teaching robes he no longer needed, telling himself I need to make sure the Granger girl has at least some faint idea what she's doing before Minerva turns her loose on our current crop of first-year students. Nothing led more certainly to utter disaster than an incompetent teacher mixed with inexperienced students combined with a room full of potential poisons and explosions.

The fact that she had spent five years believing him dead was an obstacle he hadn't allow to cross his mind. That he was about to reveal the secret he'd insisted only Poppy Pomfrey and Minerva McGonagall share was a detail he'd allowed himself to miss. After all, he had reminded himself as he stood outside the classroom door and listened to her light, quick footsteps tapping over the flagstones, very soon it won't matter. And I have a responsibility to be sure this subject is taught more than merely competently.

He'd pushed open the door, dropped an icy Miss Granger at least in part to enjoy the look of shock on her face …

Shortly thereafter, wiping Thief's Downfall from his face, he'd reflected that he'd expected her to be somewhat easier to convince. My mistake. The reflexes developed by spending months at a formative age on the run from Death Eaters and Snatchers don't tend to fade.

And now she sat opposite him in one of Slughorn's ridiculous chintz chairs, wand at the ready, demanding answers he hadn't planned to give.

He sipped his tea to buy time, studying her. In some ways, five years had changed her quite a lot. When he'd seen her for what he'd thought, then, was the last time — standing behind Potter, the only one of them quick enough to conjure a flask to capture the memories Potter so desperately needed to see — she'd still been a girl. A girl grim and worn by the burdens she'd shouldered and the things she'd seen, yes, a girl with shadows in her eyes that no-one so young should have, but still, a girl.

Before him now sat a woman. The changes were slight — the set of her mouth, the way she carried herself, the calm confidence in her eyes — but they were there. Her hair was still wildly curly, but now it was twisted up and piled atop her head in an artfully disarranged knot. She clearly still favoured those ridiculous Muggle clothes, and for her first day at Hogwarts had chosen a stunningly inappropriate ensemble of jean, thick-soled boots and a knitted top. At least it has sleeves wide enough at the wrist for her wand.

I suppose when one defeats a Dark Lord one earns the right to dress how one wants. "You look well," he said.

"Thank you. You —" She paused, but they both heard the unspoken don't. She studied him a moment. "How have you been? Have you been … ill?"

"No." It was, strictly speaking, the truth. It wasn't illness that burned through him these days, that sapped his strength and burned through whatever sustenance he could force down his throat. Already he could feel the brief burst of energy from his over-sweet tea ebbing away. It had been utterly foolish to waste his strength dressing so elaborately, it had been absolute folly to indulge the temptation to show her he was still the man who'd disarmed Gilderoy Lockhart as if the so-called expert in Defence Against the Dark Arts was no more than a student with a wand he hadn't learnt to use. He'd pay tomorrow, that was certain. But for now … He drew on the self-control and iron will that had seen him through his years as a triple agent. "No, I haven't been ill. Just in hiding."

The crinkle of her forehead when she was puzzled was one thing that hadn't changed a bit. "In hiding? From who? Everyone knows you were never really on Voldemort's side."

"Exactly." Snape sipped his tea and waited for her to work it out. Come on, Granger, you always were irritatingly clever. "Everyone knows."

"Oh! You mean … you've been hiding from Death Eaters. But … they've all been locked up. And they won't be let out until they really change their ways, and it's verified by Legilimency."

Until, she said, not unless, because even dealing with the Dark Lord hadn't significantly dented Hermione Granger's annoying incurable optimism. With slight surprise, Snape found he was glad of it. After all, wasn't that what we fought for? A world where people didn't have to be miserable, cynical, mistrusting bastards like me? "You'll forgive me if I have somewhat less than absolute faith in the Ministry's competence." His arm ached with a reminder that he had a very good reason to doubt the Ministry of Magic's claim to have tracked, arrested, and locked away every follower of Voldemort left alive.

"So you've just been lurking around Hogwarts for five years?" Her voice rose slightly, and he realised she was angry. "Letting us all think you were dead and mourning you and —"

He cut her off before she would work herself up any further. "I think mourning might be a bridge too far, don't you?"

"No, I don't!" she snapped, eyes blazing. "We did mourn you! Once we knew who you really were — are — and what you'd done, how could we not? You saved our lives, more than once. You made it possible for Harry to finish destroying the Horcruxes. You were as much of a war hero — more of a war hero — as anyone! And you never got the chance to just … just be, and know you'd won. Of course we all mourned."

"How remiss of me to deprive you all of the chance to make yourselves feel better by thanking me," he shot back in his most deadly tone, the one he usually used for the Neville Longbottoms of the world. It had the desired effect: Granger flushed pink with humiliation. Snape crushed a faint twinge of remorse — she had meant well — telling himself that adding one more to the long list of undeserved cruelties he'd inflicted on Hermione Granger was preferable to listening to any more of her maudlin maundering over how unfair his life had been. Imagine how long she'd go on for if she knew that after five years of self-imposed imprisonment to avoid the vengeance of those I deceived, I find myself in exactly the same position as if I'd spent those years sipping coffee in a Venetian cafe watching the canals turn golden with the sunset?

She'd find out eventually, of course. Now he'd revealed himself to her, that was inevitable. With luck, though, I can keep her in the dark until my funeral. She and Minerva and Poppy can have a competition for who feels the most pity for poor Severus Snape. The mental image of the three of them lined up before judges, striving to outdo each other, was almost amusing, although Snape was under no illusion he'd find it anything other than unbearable if he had to sit through it.

"There's no need to laugh at me!" Granger flared.

"I wasn't," Snape informed her. "So. Now we're all caught up, I presume you have your lesson plans already written?" When she nodded, he held out his hand. "I'll review them tonight."

For a moment, he thought she was going to refuse. Gryffindor pride and stubbornness. Finally she set her teacup down on the table and picked up her shoulder-bag. "Thank you," she said with obvious sincerity. "I'd feel a great deal better about them if someone with your experience went over them."

She held out a thick folder and he took it. "Your academic achievements are unquestionable, and I have no doubt you have prepared thoroughly." Flipping open the folder, he found the contents cheerfully colour-coded. Of course.

A wrinkle of bemusement appeared above her eyebrows. "Thank you?"

"However, the first few years of teaching can be a difficult learning process. Especially for someone young enough for the oldest students to remember them in the same uniform."

The wrinkle turned into a frown. "Well, I can't help —"

Snape held up his hand and she fell silent. "I was speaking from my own experience, Professor Granger. I was hired at the age of twenty-one. If you will permit me to give you some advice?"

"I'd be grateful for it."

That was certainly a more manageable gratitude than waxing effusively lyrical over his supposed heroics. "Dress formally, and act formally. Cultivate distance between yourself and your students. Assiduously. You are their teacher. You are not their friend, and if you try to be you will do a great deal of harm and very little good."

She looked him slowly up and down. "You're telling me to be like you. I can't be — and I don't want to, either. I understand now that you were so … so …"

Snape couldn't entirely suppress a smile as she all-too-obviously searched for a tactfully way to put it. One of my Slytherins would have managed unsympathetic, disparaging and inflexible by now. "Unkind? Unpleasant? Cruel?" She swallowed, and nodded. "Please, Professor Granger, disabuse yourself of any notion that I am, at heart, a kind individual forced by necessity to act a part with my students. And be reassured that I am not advising you to model your teaching on mine — a task to which you would be singularly unsuited, even if you were to try."

"Thank you," she said, as if he'd paid her a compliment.

By Gryffindor standards, perhaps I have. "Minerva McGonagall might be more suitable. And speaking of Minerva, as Headmistress she'll have felt you join the Hogwarts wards. She'll be expecting you." He hefted the folder a little. "I'll review this, and we can discuss your lesson plans tomorrow."

"But I have more questions — like, where are you going to review my lesson plans? Who know you're here? And —"

"In my study. Horace was never fond of living beneath the lake, and he was too relieved to ask any inconvenient questions when Minerva told him that they'd been unable to break the wards on my quarters. She knows, of course. It would have been impossible to keep it from her, given her position. And Madam Pomfrey. No others."

"I won't tell anyone," she said earnestly. "I promise."

"As good as an Unbreakable Vow, given the Gryffindor sense of honour."

She leaned forward. "I'll swear, too, sir. If you'd like."

She would, too. Give a Gryffindor a chance to make an ostentatious show of their honesty and they'll charge at it like an insulted Hippogriff, every time. "First, Professor Granger, I am no longer sir to you. Nor, for that matter, is Professor Flitwick. You are an adult, and a colleague. We are equals."

She nodded, expression contrite. "I'm sorry. I'll remember, Professor Snape." Being Hermione Granger, curiosity very quickly defeated the contrition. "What was the second thing?"

"Unbreakable Vows are very serious magic, Professor Granger," he said sternly, and if it was hypocritical of him to enjoy seeing her flinch a little like a scared student when he'd just lectured her on their equality, well, he was a hypocrite. "Don't bandy them around lightly. What words would you have sworn?"

"That I'd never tell anyone you were here."

"As well-thought out and carefully reasoned as I'd expect from a Gryffindor," he sneered.

She went white, and then colour rushed into her cheeks. He braced himself for an explosion, and was pleasantly surprised when she managed to control herself. "Please explain why."

"First, you would be swearing to keep me secret. What if your first suspicions were, after all, correct? What if I am, in fact, an impostor?"

Granger gulped, but answered, "I would have made it impossible for me to raise the alarm."

"Five points to Gryffindor."

"So I should have said 'I'd never tell anyone that Severus Snape was here'."

"Correct. But think further. What if there was some emergency? What if I was in danger, and you couldn't reach Minerva or Poppy to tell them so? You'd have to chose between, say, allowing me to burn to death in a blaze of fiendfyre or losing your own life."

She frowned. "Fiendfyre? Is that really so likely?"

He arched an eyebrow. "Professor Granger, your experience at this school was limited to seven, admittedly rather action-packed, years. I assure you, with a student body of hundreds of magically gifted and variably self-controlled students, anything is possible."

She smirked a little at that. "I do concede your point on that one. But — "

"Professor Granger, you are keeping the Headmistress waiting. We will talk tomorrow. For homework —"

In the act of rising, she froze. "You can't give me homework!"

He ignored her. "Two feet on the Unbreakable Vow, with examples of unintended consequences."

She glared at him, gave a sniff of irritation, and stomped from the room.

Finally. Snape leaned back in his chair, closed his eyes, and waited for the strength to stand.