He turned the letter over to look at the seal. Here too he was surprised, almost shocked. The familiar seal – wand crossed with a mailed fist and the tag "Toujours Pur" - had been replaced by an entirely new device. A hound, guardant or and the motto "Toujours Fidele".

He was reading the letter for the third time when there was a knock at the door and Lupin came in.

Snape was so disconcerted by the letter he blurted out the first question he had. "Black of that Ilk! Since when have the Blacks been Scottish?"

Lupin laughed and took a chair. "I asked him once what kind of Scots his family were. He said they were the kind that lived in London and only went North to kill things and make the locals' life a misery." He grinned. "It always tickled him that his family hated muggles so much but copied their ideas of nobility from the muggle aristocracy. Apparently, his great grandfather tried to get people to call him Lord Black but no one was having it. Black of that Ilk was as near as he could get, and until Sirius can get it unravelled, all his official correspondence has to be signed like that." He nodded at the letter. "Are you going to go?"

"No."

"You should, you know. You have a common aim. You both want to to keep Harry safe."

Snape scoffed. "Safe! With that mongrel. He'll have the boy dead within a month. He cannot be trusted. Have you forgotten what he did? The man's capable of anything!"

Lupin got to his feet. "That was a long time and a war ago, Severus. We both know you've changed since then and I know I have. Why not go and see if he has too? Whatever name he chooses for himself, having the Black money and influence behind Harry can only help. Whatever you say about him, no one can deny that he loves the boy." He paused in the doorway, visibly hesitant before continuing. "You say he is capable of anything, but, Severus, there was one thing he wasn't capable of – there's no way he would or could ever have become a Death-eater.

Sirius is no saint no one knows that better than me. But I know you were there when Caradoc Dearborn died, and there were probably others, no one got into that cabal without proving their commitment doing things Sirius would never have contemplated doing, and don't tell me you expect me to believe that nonsense Lucius Malfoy put about." He gestured at the letter. "Toujours Fidele – forever faithful. Not a bad motto for a guard dog."

Which was why Snape found himself outside the Spell Damage Ward in St Mungo's one Friday afternoon after his last class. And that was another thing, the dementors didn't cast spells, so what the hell were the healers playing at?

He followed a nurse carrying a foaming goblet of what was quite obviously Radcliffe's Restorer into a side room and there was Black, in a silk dressing gown looking elegantly pale and wan, like an eighteenth century consumptive poet. Snape remembered his own utilitarian wool back at Hogwarts, practical for the Scottish cold but as inelegant a garment as it was possible to imagine, and almost left. Perhaps he would have done if Black hadn't, at that moment, knocked back his potion and sneezed into a suddenly purple handkerchief.

"What in Merlin's name are they giving you that for?"

Black jumped but answered readily enough. "Mordred's Blight," he said, sneezing into another handkerchief.

"Spellshock? From Azkaban?"

"Worse case they'd seen since the war against Grindelwald," said Black, almost proudly. "They had to get some ancient witch out of retirement to treat it. You should have seen her, she looked like Dumbledore's granny. And it's not from Azkaban – mostly it's from before." He waved a hand and wordlessly vanished the purple handkerchiefs. "My dear mother had a version of the cruciatus - only lasted a split second and hurt like hell. She had a load of cutesy nickname for it – the cruciette, the cruciatino." He made a strange movement, part shrug part shudder. "Any way, seems they all added up to quite a few minutes worth of Unforgivable – hence the Mordred's Blight." He paused. "They're going to start offering free testing for it again, anyone who thinks they might be affected can ask to be seen, I reckon I'm not the only person round here with Mordred's."

"I beg your pardon," said Snape, offended.

Black waved a negligent hand. "Oh I don't mean you – though you might like to get yourself checked – no one suggested it for me at the time. I meant Molly Prewett."

"Who?" Snape was completely thrown by the direction the conversation was taking.

"Harry's friend's mother. Came last weekend to see if I was safe for her baby boy to visit."

"You mean Molly Weasley?'

Black sat back in his chair. "She used to be Mad Molly Prewett, United Kingdom All-Comers Champion Dueller, and they reckoned she was a shoo—in for the Europeans and maybe even the Worlds. She was a demon in the ring. Now look at her, terrified something is going to happen to her kids if she takes her eyes off them for 30 seconds. You know she got ambushed by Dolohov and his nasty little friends? She fought them off but she took a hell of a beating. If anyone was going to get Mordred's after that, it's her." He swiped at the side of his nose with his whole hand, a gesture that reminded Snape of something he couldn't quite bring to mind. "Did you ever see her fight? I did and she was a terrifying. James and me tried to learn the Prewett Point Catch all one Christmas holiday and never managed it."

Black sneezed again, his handkerchief so dark purple it was almost black. A silence fell. After that torrent of words (surely Black wasn't nervous) he seemed to have run out of words. He gestured to a chair and Snape moved it slightly so he had a direct route to the open door. He sat. He'd let Black babble to his heart's content and then decide what to do with the information.

"Thank you for coming," said Black eventually. "I know you don't want to be here but I also know you've come for Harry. You probably don't want my gratitude, but you have it anyway." He sighed and looked down. "I don't recommend Azkaban as a mental health cure, but it made a lot of things horribly plain. The dementors, they steal your happy memories and leave the rest for you to watch happening over and over again. Including what we did to you. I won't make excuses, but I am sorry. We ganged up on you and that wasn't right. I was going to apologise, even before I found out you'd taken Harry under your wing." He grinned ruefully. "Of course I expected you to be a complete dick about so I could go on disliking you but it looks like we've both had a change of heart."

A long silence fell. Snape had a sudden memory of his written conscience, still pinned to the door between his quarters and the teaching laboratory. He had hated Black for most of his life, he still did, he thought, but compared to what he needed to do for Harry, that couldn't be allowed to matter.

"We need not speak of that now," he said, repressively. "I just want to know what your intentions are towards Harry."

"I'm going to adopt him."

"What?"

"I knew I'd never have children of my own, even as a kid I knew that. The Blacks are rotten in body, mind and magic. Do you know what the average life expectancy is of the men of my family? 63 and that doesn't include the ones who died violently. The line ends with me and continues with the decent, healthy magic of the Potters and Evanses. As soon as I'm certified fit, I'm adopting him, blood, bone and magic."

They sat for a long moment in silence. "Has Lupin told you about the blood protection at the muggle's home?"

"Yes, and we're going to work to keep that up. As soon as we know how long he has to stay every year, I'll bribe 'em to keep him for just that long. I thought we could convert his bedroom to a little suite. Fill it full of fun and interesting stuff for him to do, and then, the moment he fulfils the residency requirement, we get him out."

"Two weeks, 3 days and 17 hours," said Snape. "Filius Flitwick checked a few days ago for me. If we say two weeks and four days for safety, that should cover it. Do you have somewhere safe for him to go?"

Black nodded. "I've hired a team from Gringotts to clean out the Black family home in London. It's a hideous, dark-infested dump, but it's got more protective charms than just about anywhere but Hogwarts. I'm hoping to make it fit for him by the end of term." He cocked his head on one side and considered for a moment. "You'd be welcome to join us."

"Me!" That was a real surprise. He'd hardly thought this new rational Black would go that far!

"Harry would love it and there's loads of room. There's even a pre-war Dagworth-Granger potions lab in one of the cellars. Been locked down since 1939 so there's probably all sorts of stuff in there."

And wasn't that a temptation. A potions lab uncontaminated by the nuclear fallout that got everywhere, even magical enclaves.

"You can't possibly want to share a house with me!'

"Perhaps not, but Harry would love it, and that's what matters to me. Like I say, the house is huge, you could have your own set of rooms, we wouldn't have to see each other unless we wanted to, Harry would have another highly competent wand to hand and.. well… look at us! We're sitting here, having a civilised conversation, surely we can keep on doing so."

"I don't…"

"You don't have to decide right now," said Black, hurriedly. "Take a few days to think about it and there's something else you ought to know. I've told Albus and he says you can be trusted. The curse-breakers found something more than usually vile at the house. It's a horcrux."

Snape recoiled.

"It seems my poor, silly little brother had a change of heart and stole it from You-Know-Who. Doing it killed him." Black's lips compressed and he looked away. "Daft sod never did have the sense he was born with and he paid the price."

Snape had barely known Regulus Black who had been a couple of years below him at school and had been the worst possible thing to schoolboy eyes, a sneak. Though thinking about it from the vantage of his many years as a teacher, being a tattletale was probably a viable survival strategy in a household which used the cruciatus as a disciplinary tool.

"Albus is putting together a small team to hunt down the rest of them. There's no way You-Know-Who would have made just two, the arithmancy is all wrong. We're running the hunt out of the house, as soon as you're in, I'll tell you where it is."

"I'm in." There was no way he was leaving this to Black.

"Right, I'll give you the address as soon as the Gringotts team has finished. Believe me, it's not a place you want to visit until they're done. It wasn't just the Horcrux, there was a Torment Talisman in one of the bedrooms and some renegade Black had carved a particularly nasty rune cluster under my father's desk. No wonder he was mad as a hatter

If they're not finished in time, I'll take Harry abroad for a the Summer, let him be a kid at the seaside somewhere. Might do that anyway, since those lousy muggles always left him behind when they went on holiday."

Snape considered for a moment. If they were going to do this, then there had to be a complete sharing of information. And really, Black was being uncommonly courteous and reasonable.

"Harry has begun to have music lessons," he said.

Black nodded, "Yes, he told me. You're hoping he might be an enchanter, aren't you? Oh, there's no need to look like that, no one is telling tales out of school. My dear old mama had hopes of Reggie. He had a lovely voice as a child: after puberty he sounded like a rusty gate."

He looked down and shook his head, as though shaking some unpleasant though away. "You know Mum – Mrs Potter – had a theory about the Dark Arts," he said. "She reckoned they always exact a price. Not just the sacrifice demanded by the rituals, not even the mental….. contortions you have to engage in to want to do them in the first place. She thought that whatever you do that way, you pay a price and the price goes up the deeper you go. They start small: you become allergic to your favourite food; your pet dies; an athlete gets a broken bone that never heals right that sort of thing. And they just get worse and worse until you lose things that really matter, like family intelligence or fertility. Look at Godolphin Goyle, went to school with my grandfather and had the highest marks in his final exams ever recorded, joined Grindelwald and his son scraped through his Newts and, according to Harry, his grandson is barely literate. Or take the Malfoys, Abraxas had a brother and two sisters, Lucius had a sister who died just before her Hogwarts letter would have arrived and Draco is an only child. Or the Blacks – there were five of us in my generation and we've only had two children between the lot of us. It would be so bloody ironic if my family's obsession with gaining power through the Dark Arts had cost us a genuine enchanter."

He sighed. "Mum was working on a proof when she died. I have her working notes in my vault at Gringotts. Remus and I are going to try to finish it. The arithmancy is promising but far beyond my Newt but if I have to, I'll call in one of the experts from India. If they can't solve it, they can teach me enough so that I really work on it." He looked at Snape earnestly. "It sort of feels right, even if I can't yet prove it. Know what I mean?"

Yes, Snape knew what he meant. The moment when the usual recipe called for an ingredient to be chopped and you knew, you just knew that it should be crushed instead. He thought back to his own first dabbling in the Dark Arts, how how afterwards he always seemed to be slightly too cold for comfort. Perhaps he'd been lucky that most of what the Dark Lord wanted of him was information and his skill as a potioneer. He'd certainly become more irascible. He'd put that down to the pressures of his double life, but perhaps not. Hell, perhaps he'd better get himself checked for Mordred's Blight – Merlin knew how many spells he'd taken, and the symptoms of the Blight included volatile emotions and poor impulse control, which, now he came to think about it explained a lot about Black too.

Black was looking at him solemnly. The man was powerful: magically, financially and socially. He was behaving reasonably and talking intelligently and calmly. Perhaps it was worth the attempt. Snape knew his days as a spy were over. The Dark Lord, if and when he returned, would know him for what he was. Better then to take the fight to him in ways he would not expect.

Snape leaned over and held out his hand. "I am in correspondence with Professor Kaur of the Mumbai School. Perhaps we should approach her for her assistance."

Black took his hand, shook it and grinned. "You ever seen Casablanca, Professor?"

"Yes, my father was a muggle and my mother loved old films."

Black put on a Humphrey Bogart voice. "Louis, I think this is the beginning of a beautiful friendship," he said.

Startled, Snape couldn't help but laugh.