Knockturn Alley is full of furtive movement and mutterings even though it is thirty minutes until the newly-imposed curfew and bitterly cold. It is the first Saturday in 1981, and the street has well-hidden inlets and outlets; the people flow through like a river. No one wants to catch the ire of the Aurors who are, even now, certainly watching. Most of the legal transactions still have the sly movements of the illicit; most of the illicit transactions have the easy grace of a carefree conversation. Everyone's head is covered in hats, scarves, hoods both to stave off the cold and to disguise identity.

That's how Severus hides: hood pulled high, collar turned up against the chill, stubbled chin and telltale nose hidden behind a lumpy wool scarf. It's cold enough to warrant it. He's looking at a fogged window at an assortment of cursed books, watching one drag itself to and fro past the others-the one that shakes, the one bound in human skin, the one whose gently shifting cover pattern could hypnotize if you weren't careful.

The books are a pretense; his real focus is the reflection in the window of the people as they move up and down the street. He straightens when he sees his target: a bright yellow scarf, catching the dim streetlamps in the snowy gloom, strolling slowly down the alley. He jerks his head as the yellow scarf walks past, tugging his own collar tighter, making sure the tiny brass star pin-his own marker for his partner, nicked from a pawn shop-is exposed. He turns, and they fall in stride, looking straight ahead.

"You're late," Severus mutters.

"You'll wait if you need it," he drawls. "For your little haemophiliac customer, you said? Sad story." He sounds as if he's heard about a dozen of them today and gives credence to none. "It's five galleons, now. Do you have the money?"

"Yes," Severus huffs, the word making a puff of mist in the cold air. He had hoped for a discount, with the whole cloth tragedy of a sick child woven in, but clearly struck out. Perhaps the man was raising his prices to charge for the lie, as well.

What they are doing is not precisely illegal, which is why the item is not delivered by one and the payment taken by another to thwart law enforcement. But this transaction is also not entirely above-board. Were a Ministry official to inquire after it, certainly no tax would be paid, and Severus knows for a fact that the brewer would not be certified. There are a number of reasons not to be certified, though; one could be unable to find a Master to apprentice to, or one could be a registered werewolf or vampire or half-breed of some description, or one could simply lack the galleons.

Even galleons themselves are muffled where Severus holds them between his fingers, and the flagon of potion is swaddled in dirty canvas. They pass hand to hand with ease, and Severus takes the vial easily even though nerves have his fingers shaking. He's bought ingredients from the black market like this, but never a finished potion before, and it feels less like a transaction between fellow professionals and more fully illegal, which means more frightening, with the Aurors permitted to attack with Unforgivables first and interrogate later.

But there's more he's supposed to get, more than just the vial. "Your supplier-" he starts.

But his companion has already turned to go into a dimly lit shop door. The shopkeeper greets the man with a thin smile and the door shuts behind them both, and Severus fights the urge to look after, to look around at all. Looking around is worse than walking alone, but his heart is still pounding. He takes a deep breath and lets it out slow, through his teeth, so it doesn't make a huge puff of steam; it was clumsy to ask like that, clumsy to pry so openly at the supply chain when he'd only just won the dealer's trust enough to sell. He has to keep his gait even, step by step, soles slipping on the icy cobblestones. Well, half of Dumbledore's task was to get blood replenisher. He has blood replenisher. The other half-meet with his new contact and begin some kind of work with them in person-will be more painless. It has to be.

Near the end of the alley he slips into a doorway and, spine rigid with the effort it takes to not glance backwards, he disapparates.

The designated place Dumbledore had indicated is not so far as it might be; he makes two stopovers before coming to rest along the foggy, moonlit street. He walks five long blocks, takes two left turns, and crosses a street to ensure he isn't being followed despite the fact that there is no body in the darkness trailing him, no footsteps in his ear to betray a follower. It helps calm him, and it is perhaps the only spycraft that he'd managed to think of on his own that wasn't entirely lifted from a pulp novel. His heels are muffled on the sidewalk by snow and charm, and his dark cloak sucks in the light. He feels like a shadow, and is comforted by the thought.

The dingy, dim muggle lane with its dirty shutters and spindly trees comes to an end and there, in the dimmest corner, is the address he was given. One light is on in an upstairs room. Up the stairs to the door, and Severus pauses at the threshold, tugs his hood closer to his cheeks, and knocks.

The door opens of its own accord. Charmed, it must be. Or a trap. He could walk away. It would be safer. Severus thinks of the light upstairs. They must have heard. Might have opened the door using their own wand. It could be an Auror ambush, or a Death Eater ambush, or an Order ambush from those who embraced the more brutal methods Dumbledore claimed to not endorse.

Severus has scrounged in the dirt for as much information as he could for Dumbledore for over a year: it was, all of it, thin, barely sufficient, little of it actionable. Then, on new year's eve, an owl carrying Dumbledore's sprawling script: Acquire a blood replenisher potion and meet your new contact, I have an assignment uniquely suited to your skills. This is your opportunity to gain my trust- and the date, time, and location, this anonymous, run-down home. He had barely managed to find someone who would sell him the blood replenisher in time for the meeting.

Severus decides that he wants Dumbledore's trust. It's the only hope he has of surviving this. He strides across the threshold and shuts the door behind him, throwing the bolt.

Warm light is pouring down the stairs in shattered shapes, carved by a banister, but no light is on in the first room, a parlor with an arm-chair and a fireplace. Dimly through a doorway he can make out a kitchen. He waits to hear someone call or speak, but no one does. When no one appears, he whispers, "Hominem revelio."

His senses expend for a swooping moment and-yes, someone is upstairs in the lit room. He begins slowly moving toward the stair. A floorboard creaks beneath him and he pauses, briefly.

Someone is humming. The tune is half-familiar, half-remembered, something from the Muggle radio from a long time ago.

Two more steps. Only one room is illuminated, the one he saw from the street, half a bookcase and a desk visible behind the banister. No person. Two more steps, and still nothing. Three more, and he's at the landing. Four more-

A door with no light behind him flies open and there's a wand stuck in the back of his neck. "Don't try anything," a woman's voice demands. "Were you followed?"

Snape's head turns slowly. Something very odd is happening in his gut. The seller's voice had been an intentional cipher, but this one, that voice is- "Do I know you?"

She scoffs, then. "I said, were you followed?"

"I wasn't followed," he says. He could shoot a hex over his shoulder, could sweep her legs out from beneath her, could run. But this is about trust. "I have what Dumbledore asked of me."

"All right." The pressure comes off the back of his neck. "You can turn around."

He very nearly doesn't want to. He stares for a single, flat moment into the opposite room, lit so well, and curses himself for being tricked, for having a secret, for defecting to Dumbledore, for being so damn predictable.

Then he turns.

There she is: red hair, green eyes, anger, and the reason Dumbledore hadn't told him the name of the handler who would meet him. "You," he says, pushing all the loathing he has for himself into his tone. "Dumbledore didn't say-"

"Dumbledore didn't say because you wouldn't have come," Lily Potter says. "Frankly I wouldn't have believed it myself if you weren't standing here."

He had begged-on his fucking knees in front of the old man-for her life, this exact woman's life, almost a year ago. Dumbledore had taken the defection and assigned it a price: information. He had paid it, over and over again, through a Protean charmed quill and through the Auror Bones and, very rarely, Dumbledore himself. Too much obvious, direct contact was dangerous to Severus himself. Dumbledore cared at least that much for his life.

He had wondered, briefly, if it was meant to be an Auror sting to lock him up. While gray market potioneering could lose his certification if it happened too many times, it wouldn't put him in Azkaban, it wasn't really any more illegal than the woman selling homemade pasties by the train station, and Dumbledore had far worse against him.

Far worse that was now standing before him. Severus spits on the floor at her feet.

Lily wrinkles her nose and glared down at the little wet patch on the carpet, then returns to glaring at his face. "Are you done?"

"I'm not working with you," he says hotly.

"Fine," Lily says. "I told Dumbledore you we're better suited to Azkaban anyway, when he gave me this assignment. Glad to know I'm right."

The idea that she didn't want to work with him-that she had been assigned when all of this had been to protect her-and her prophecied son and her dreadful husband-that she might be right- "Is that what you think," he hisses, stepping closer. He has grown since the last time they had stood so close together. He has also learned many things, learned to use his voice better than just to shout, learned to imply violence instead of just reach for the blunt tool first when anger flared, learned to be quick and smart and keep a level head in a fight, which maybe this was shaping up to become. He could look down his long nose at her, eyes narrowed in disdain, thinking you're nothing to me and make it plain on his face without saying a word. He keeps his tone just barely level through sheer force of will. "You know what I am, then. Perhaps you should think twice before threatening me."

Her wand must be up her sleeve, the way her finger twitches, as if considering bringing it to her hand. "I don't think you're going to hurt me," she says, voice tight but even.

"The Dark Lord has murdered mothers before, witch."

"I know he has. I don't think you are going to hurt me." Her eyes are fixed on his, even, open, brow knitting back together, but not in anger-in frustration, as if he were being particularly dense. She pushes past him, toward the light. "Come on. Let's sit in the study. Don't touch anything. This is the house of a Muggle on holiday so I'd ask you not to make me stage a break-in for him."

He could leave. He could leave, right now, throw the swaddled potion down a sewer grate, disapparate, go home, get blind stinking drunk and go to sleep on the couch. He could do it right now and likely wouldn't even suffer for it. Dumbledore wasn't the kind to punish, not the way the Dark Lord is.

He follows her into the study. She takes the seat at the desk. There is a fat floral armchair that Severus would rather set on fire than sit in, so he stays standing.

"Our assignment," he says, with all the disdain he can muster.

"Yes. Right." She pulls a piece of thumbed parchment out of her pocket and sets it on the desk."You've got your Mastery and certification, you're probably brewing, right?" She doesn't wait for an answer. "There is an artificial shortage in medicinal potions ingredients, Ministry's throttling imports and increasing hunting down home-herbologists growing ingredients. And there's an all-time low of potions masters." Her eyes go narrow and sharp, as if daring him to say anything about why she isn't one-the marriage, the baby, her blood status and the fact that most potions masters would hesitate even in peacetime to take on a mudblood.

Severus is glaring at the window, at his own reflection and hers. He flicks his fingers at Lily as if he doesn't care, gesturing in a loop. "Get on with it."

Her hand on the desk becomes a momentary fist, but then she goes on. "The biggest pinch is blood-replenisher. Even St Mungo's is feeling pinched on that one. The only place that can reliably stock medical potions is the black market and the prices-"

"You owe me five galleons, by the way," he interrupts.

"Five?" She looks shocked. "Last week the going rate was three."

"I suppose they aren't giving me the new customer discount that they offer to Order members," Severus says bitterly.

"Not to slimy bastards like you, anyway," she retorts.

He moves to the door. "Tell Dumbledore-"

"Oh, hell, sit down Sev." She passes a hand across her brow. "I'm sorry, all right. That was uncalled for. You did what we asked." And then she starts digging in her pocket. "I don't think I have five. I only brought what I needed. I've got a few quid-"

"It's fine," he says harshly from the doorway. He can't exactly afford all five of the galleons but he's not about to beg for two. There is enough rice in the cupboard, he won't starve.

She produces three coins and places them in a neat little stack on the desk, as if asking him to come back in. He does. They're warm to the touch when his hand covers them-the warmth of her body, he realizes uncomfortably. He inspects one. It's so bright, it must be fresh from the bank, but the mint date is 1716.

Potter gold, then, minted and then put in a bank. That, too, he swallows, and shoves the gold into his pocket. He can feel her watching him and tries not to allow the ugly flush that he knows is creeping up his stubbled neck to reach his cheeks.

"Anyway," she says, clearing her throat and reverting her gaze to the well-thumbed note. "Fully half the potions the Order managed to source have turned up tampered with or outright poisoned. And they were poisoned really well, even I had trouble when I went through our stores."

That is interesting. Some Death Eaters had died of tampered black market potions, and they suffered the same difficulties the Order had. Detecting the tampering was a feat in itself, Severus knew firsthand. "And you want me to inspect further? Follow up your work?"

"No," she says. "Dumbledore wants us to trace the tampering back to their source. Figure out who's doing it, and why. Maybe even stop them, if we can."

"I would sooner suggest you stop taking medical potions," he snaps, rattled by the ambition of the task-and the word us. Himself and her, working together; not the occasional report, but real work. Low risk spy work compared to the passing of information that he had already done-that would get him killed, this could be played off-but still valuable or he wouldn't be doing it. But then again, he had never been a spy before. His forearm itches, at that thought. He doesn't reach for it.

"People are dying, Severus," she says, deadly serious. "We can't trust anything but charms and you know well as I do that potions are better for the worst of it. People are dying and will keep dying and you and I are the best brewers the Order has. This is our assignment. Do you accept it or do I have to tell Dumbledore that I'm working alone?"

He resents that. It's not as if he had a choice regardless. "Your first sample, then," he says stiffly, dropping the cloth-wrapped vial before her on the desk. "I take it you will require more?"