"What did you do to yourself?" Severus asks when she arrives that night to begin brewing the Polyjuice.

"What do you mean?"

"You didn't wave your hand in the air once today. And you worked with Weasley instead of Longbottom."

"I wish you'd stop calling her 'you' – I'm a grown woman and a member of staff and she's your student."

"The pronouns get as tricky as the verb tenses."

Hermione doesn't think they do at all, and concentrates on her chopping.

"Was my Pensieve involved?" he asks, noticing that she's brought it back.

"Sometimes people can tell us things until they're blue in the face but we can't really believe them until we see with our own eyes."

They prepare ingredients in silence for a while, then he says, "I'm thinking of having you – her – work with Malfoy. Now that she's minding her own business and not annoying people."

"He won't like that."

"He's a spoiled little wanker."

"He is that."

"But he isn't in your time."

"No. In my time he's been through hell and back and it made him a better man."

"That won't happen this time, if we do this right."

"He was worried about that."

"Rightly so. He runs with the wrong crowd, just as I did at his age." He shakes his head. "But a Gryffindor girl as my lab partner didn't keep me from going bad."

"Maybe she was the wrong Gryffindor girl."

Severus frowns at her. "Explain yourself."

"What you said was stupid and hurtful but you were a teenage boy. Teenage boys say stupid, hurtful things all the time. And teenage girls forgive them. If Lily Evans chose to end a friendship of that many years over something so trivial, that's on her, not you."

He glares at her. Does this insufferable woman know everything about him? How does she know? Does becoming a portrait mean you lose all sense of privacy and impulse control? After a few minutes of doing to a toad's tongue what he'd like to do to hers, he mutters, "It wasn't trivial."

"It was. Malfoy called me Mudblood for six years and I forgave him – as I told your portrait, who was still wallowing in guilt over that bloody Evans girl even after he was dead."

"Don't you dare speak of her that way. You know nothing about her. You know nothing about any of this," he says in a voice that would have terrified her five years ago.

"The prophecy, you mean?"

"I killed her."

"Tom Riddle killed her. You were just one of the weapons he used."

"It was my fault. Mine."

"You had some share in the responsibility, but your guilt for decades after was all out of proportion," she says gently. "And Albus Dumbledore fed that guilt so he could turn you into a weapon of his own. He used you as cruelly as Riddle ever did, and you let him, because you blamed yourself for something that was never more than tangentially your fault."

Severus chops fluxweed as though the fate of the world depends on the uniformity of the pieces. Hermione watches him, understanding that he clings to his guilt as the only part of Lily Evans that's left to him, and he can't let it go.

"You're here to kill Riddle," he says in clipped tones a few minutes later, "not to redeem the tormented Byronic hero you seem to think I am."

"I am here to kill Riddle," she agrees, "but also to try to keep Malfoy from becoming a racist arsehole. Also, if you'll let me, to be your friend while you're a living man instead of a dead portrait."

They continue brewing and the silence stretches out between them, but it doesn't feel awkward or oppressive. She's so different from the Granger he teaches in Potions class. She's calm and self-assured and doesn't seem bothered in the least by anything he says to her. She says she wants to be his friend, but in truth she behaves as though she already is.

But why? She's going back to her time as soon as the Horcruxes are destroyed. What's the point? He won't see her – this her – for another seven years. He'll go on teaching her younger self and she'll go on breaking rules with Potter and earn a dozen NEWTs and marry some Weasley or other. She won't be the woman who lost everyone she loved in a war and befriended a dead man because there was no one else left.

And he isn't the man she knew in her time. He's no hero. He hasn't risked his life, faced torture and death to work for victory over the Dark Lord. He hasn't let the entire wizarding world think he was murdering scum while he secretly protected students from torture. He hasn't died to save them all. All he's done is kill the only woman he ever loved.

He won't do any of those things if they succeed in destroying all the Horcruxes. And he won't have to stay here at Hogwarts, waiting for Dark Lord's return. He can leave, start his own business, start a new life, never see Albus or Potter or any of them again if he doesn't want to. Or Granger.

He glances at her as she stirs the contents of her cauldron, concentrating on the number of stirs. The steam from the potion is making her straightened hair start to curl, and she looks more like the Granger he saw in her memories. More like the girl who will grow up and forget him, and less like the woman whose magic twined sinuously around his own as they dueled.

He's never experienced that before, but he's read about it, and heard about it from others who have. As different as they are, their magic shouldn't be that compatible, and yet clearly it is. Does she know what happened? The Granger who is his student is an open book, displaying her emotions for anyone who cares to look. Not the adult Granger. She's not practicing Occlumency, but she has learned to school her features.

The rod stills its clockwise motion and begins stirring the brew anti-clockwise. Granger resumes her silent counting.

When they dueled, he could feel her desire, but he's seen no hint of it since then. Did he imagine it? He could suggest dueling practice, and find out. He extinguishes the flame under his cauldron. What would be the point? No, the sooner she goes back to her time, the better.

"Know what I feel like doing, Granger?" he asks as she removes her cauldron from the flame.

"What do you feel like doing, Snape?"

"Driving a basilisk fang through a piece of Tom Riddle."

"What, now?"

"No time like the present. I'll get the ring while you get the locket."

"All right," she says, and hands him a basilisk fang.

They walk in silence to the castle gates.

"Try to stay away from the mutt. You don't want to get fleas," he says, and apparates away.