Here's someone who has a little more of an idea what to expect, from the school at large if not from the Sorting Hat in particular. 

At the moment the hat drops onto his head, Christopher is wondering if he'll be able to talk it into putting him in Gryffindor, or if he'll have to bribe it somehow. 

Well, you're not exactly helping your case with that sort of scheming, it comments. There's a house for people who'll do anything for the sake of their reputation, you know. And it's not Gryffindor. 

"Please," he whispers. "It—it doesn't have to be Gryffindor, just—anything, anywhere but Slytherin. I'll, my dad'll hate me, please."

Hmm, let's see. You're smart enough, but...no, there's no great love of learning there. You'd never fit into Ravenclaw. Hufflepuff, perhaps. Many witches and wizards have made great friendships there. But not you, I think. You're searching for a different kind of friendship. And you'll find it in...

"SLYTHERIN!"

Everyone's watching. This is his first impression on the entire school, including his new housemates. Because, apparently, he's a Slytherin now. The same house as the Dark Lord himself, the house that was home to so many Death Eaters. Maybe home to the next evil, the newest monster that's going to terrorise the wizarding world. 

Christopher doesn't think he can manage a smile, but he can keep his back straight and hold his head up as he walks over to the table full of people in green. The important thing, with monsters, is not to let them see you're afraid. 

People are talking around him. Someone addresses him — she says his name and everything — and he understands "Who are your" and then nothing else that comes after it. 

He looks at her blankly, and she waits for almost a full minute before she moves on to the next first year, and people mostly don't speak to him after that — he catches the word "name," and then the word "family," said by a boy at least twice his size who's looking at him sideways, but people don't try to speak to him as far as he can tell. 

He eats. (There's so much food, here — there might be less, after the first night, but even if there is less there will still be enough, he tries to remind himself, he doesn't need to keep careful track of how long it is until they get their next allotment.) 

He follows the other first-year Slytherin boys to their common room, where a girl and a boy who look like they're upper-years give a long speech that he understands very little of, and then to their dorm. That first night, he's not so nervous that he doesn't sleep. 

Yes, his father was Aimery Parsons. Yes, that Aimery Parsons. The Auror. 

He answers in monosyllables and pays just enough attention to the conversations going on around him to learn everyone's name and figure out how they're all related. It helps that bloodlines are seemingly all anyone wants to talk about at the feast. No surprise, nearly the whole table is full of purebloods with just enough half-bloods to make up the numbers. There's not a Muggleborn in sight—at least none that'll admit to it.

He vaguely notices when one of the other first-years point-blank refuses to answer a question about his family, just staring at the girl who asked until she gives up. Christopher's not sure if that's a really gutsy move or a really stupid one.

He memorises the password to the Slytherin common room and listens carefully to the talk the prefects give them and waits until he's pretty sure everyone else in his dorm is asleep to sneak out and sit staring through the window at the dark waters of the lake.

It's quiet, almost peaceful. He has space to think for the first time since the Sorting. 

Dad is going to be disappointed. There's nothing he can do to change that. Aimery was assuming his only son would follow him into Gryffindor, and he'd have been at least a little disappointed with anything else, even Ravenclaw. Hufflepuff would have been acceptable, barely, but Slytherin? Christopher will be lucky if he doesn't get a Howler in the post in the next few days. He'll send a letter first thing tomorrow morning; it'll be better if Dad hears it from him. Not much better, but still.

 An eel swims past, bulbous eyes swivelling dispassionately towards the small boy in the window and then away again. 

He doesn't feel evil. He's not sure how he'd tell if he was, but he doesn't think he's going to decide Muggleborns are inferior and go on a killing spree, or come home for the holidays and torture Grandpa. So being in Slytherin probably doesn't mean you're evil right from the start. Maybe it takes longer to work than that, and he'll think torturing Muggles is fine by Christmas, or the summer holidays, or by the time he graduates. 

Maybe it's not magic at all, just people. He knows a lot of the younger kids are just repeating things their parents say, or things they've heard from older students. Spending seven years living with evil people is probably enough to make anyone a little bit evil. 

He curls up a little tighter, shivering. It's cold in here, and being next to the window isn't helping. 

Okay. Things could be worse. He could be a Squib, which is just about the only thing that would disappoint his father more than being a Slytherin. And if the thing where Slytherins all turn Dark is just about what friends they have, and not about the Sorting Hat picking all the evil ones, then maybe if he makes enough friends from the other houses he'll be okay. If he's really careful and clever and puts a lot of work into it, he might even be able to stop some of the other Slytherins turning evil. 

Make friends, don't turn evil, save the world. No pressure. Actually, that feels weirdly comforting under the circumstances. 

The next morning, his inkwell (he doesn't know why they use inkwells here, but maybe McGonagall had explained it when she took him to Diagon Alley and he just hadn't understood) is broken, and almost all of his clothes are ink-stained. 

He cleans up as well as he can, and checks his books to make sure none of the pages got splattered, and locks his trunk and takes the key with him when he goes down to breakfast. It's not like he would have been able to take notes anyway. 

His first class in each subject goes — about how you'd expect them to. Some of his teachers are better than others. Flitwick speaks very quickly and doesn't seem to notice how blank Sasha looks; McGonagall looks disapproving of the stains on his clothes, asks him questions he doesn't understand and definitely can't answer; Snape hovers and snaps at students but aims his disapproval at the Gryffindors on the other side of the room. He can mostly figure out herbology; Sprout gives practical demonstrations as well as verbal instructions, and doesn't seem to mind that he doesn't raise his hand to answer questions. 

He's the smallest person in the first-year Slytherin dormitory, and he knows when people hate him, knows on a level he couldn't verbalize even in Russian how to tell when the words you don't understand are aimed to hurt you.

After three days he stops sleeping in his dorm.

Nobody's attacked him yet, but mudblood, whatever it means, sounds uncomfortably like жид sounded when he was — not home, that wasn't home, this is home now — and he isn't willing to let his guard down, not that thoroughly. He stays awake and does homework in the common room at night, copies out words from his textbooks that he thinks are the ones the professor was using that day in the best handwriting he can manage, and sleeps in his free periods, curls up under staircases where he won't be in the way, or under tables in the library, or slumped over his desk in History of Magic, where nobody else is paying attention either and so it won't be conspicuous that he isn't. It's not anywhere near enough, but he'll take what he can get, and make up for it on weekends as much as he can. 

Christopher is planning to make friends with everyone in his year eventually, but the weird loner who never pays attention in class doesn't seem like the best place to start. Instead, he picks out the boys who are popular, but not the centre of attention, and gets to know them. Most of them turn out to be pretty normal kids who've been raised by traditionalist wizarding families and barely know anything about Muggles other than what their parents taught them. He doesn't try convincing anyone just yet, but he does nice things for them, like helping Adrian Pucey with his Transfiguration homework. He starts running errands for some of the older Slytherins, too. It can't hurt to be on the good side of the prefects. 

In the classes they share with other houses, he looks out for people who wouldn't mind being friends with a Slytherin. He's not expecting much from the Gryffindors, but Hufflepuffs are supposed to be friendly, and Ravenclaws are supposed to be smart. Maybe they'll be smart enough to figure out the thing about not all Slytherins being evil to start with.  

They share Charms with the Hufflepuffs, and Diggory doesn't seem to mind having Christopher next to him. 

Normal people work differently to Slytherins. Christopher knows this, even if he couldn't put the difference into words. The tricks that work to make friends with one aren't the same as for the other. 

He waits for a charm Diggory masters before he does, then: "Hey, would you mind showing me how you did that? I can't seem to get it." 

"Of course — here, you're moving your shoulder too much, the motion should be mostly in your wrist." He demonstrates. 

He copies the motion closely and gets the spell on his next try. "Thanks! I wouldn't have spotted that on my own." 

"No problem, glad I could help!" 

He does seem significantly friendlier to Christopher after that. 

Great! Christopher's plan to make non-Slytherin friends is off to a good start. 

On Fridays, the first-year Slytherins have Defence Against the Dark Arts with Professor Kennilworthy, who's brand new to the school and arrived at the same time they did. He's a tall man with a bristling moustache and shockingly orange hair which seems to stand up on its own. He has a tendency to go off on tangents about his adventurous youth every few minutes. He seems to have had an encounter with practically every entry in Fantastic Beasts And Where To Find Them. 

The students quickly discover that Kennilworthy likes to stride stork-like around the classroom as they take notes, bending down every few desks to peer at a student's handwriting before moving on. 

Kennilworthy is obviously engaging — if Sasha could understand more than two words out of any given sentence he's sure he'd be fascinated — and animated enough that it's not hard to look engaged.

He's already aware that his handwriting in this alphabet looks like a child's, that he writes too slowly, and that he has never used a quill in his life and isn't really sure how to start; he can barely read it himself. He's guessing wildly at what he should take notes about, but copying whatever's on the board is probably a good bet.

He shrinks back, just a little bit, only as much as he can't suppress, when Kennilworthy bends down at his desk. 

Just as he has with every other student, the professor gives a dismissive "Hmph!" and straightens up again. 

By the end of the class, he's clearly running over time and has to shout their homework assignment as half the class is already out of the door. 

Sasha steals as much time as he can to tuck himself away in a corner and sleep and it's not enough, his reaction times are getting slower and his handwriting and reading comprehension are getting even worse, but — but he doesn't understand the word that a Ravenclaw girl says when she's looking right at him but he knows that dismissive tone, he keeps hearing the word Mudblood tossed around and he doesn't know what a Mudblood even is but he knows that sneer. He tries sleeping in his dorm again and he can't, the part of his mind that he can't turn off is too sure that he's not safe here. 

He spends a slightly ridiculous amount of time in the library. Madam Pince is sharp but as long as he's quiet and doesn't damage the books she likes him well enough, even if he does spend that time sleeping under tables and not studying. Nobody bothers him here. He doesn't write down which places are safe, but he keeps a careful mental list and the library goes on it. 

He turns in his homework. It's abysmal, Sasha knows it is, but it's done and that's more than some of his classmates can say. He's vaguely aware that Snape is his head of house, and he's supposed to go to him if he's having problems, but the look on Snape's face whenever Sasha's in his classroom makes the chances of Sasha ever actually doing that almost zero. By Tuesday his eyes ache, faintly, when he tries to focus them; he watches what other students are doing and copies them rather than trying to read the instructions on the board. 

By Friday in Defense class, he's tired enough that no amount of effort from him or animation from Kennilworthy can keep him looking focused. 

What about a professor leaning over his desk and asking why he's stopped taking notes? 

"...Michaels? No, Michaelov? Something like that, isn't it?" 

"Mikhailov." He wants to sound like he cares. He just sounds exhausted. He's still holding a quill, but he can't seem to get his fingers to move the way he wants them to; what he has written today is completely illegible even to him. 

"Mikhailov. Mikhailov, why haven't you written anything down for the last fifteen minutes?" Kennilworthy demands. His voice rises in pitch. "This is important information, young man!" 

He understands his name, and "why" and "you" and "last" and "is", and nothing else in that sentence. He doesn't stop his hands from shaking. Partially because he's too tired and partially because he just. Doesn't want to.

"I —" 

He doesn't know how to finish that sentence. Doesn't know the English words, doesn't know what he'd say if he did. 

"Well?" Kennilworthy waits another few seconds for a response which is not forthcoming. "Right then!" He abruptly straightens from his bent position. "You can explain it to me in detention."

Giving Sasha a crisp nod, he moves on with the rest of the lesson as though the matter is settled. 

Okay. He's picked up the word detention, by now. That could have gone worse. It means he'll lose sleep tonight but it could have gone worse, at least Kennilworthy isn't paying attention to him anymore, even if some of the other students are looking at him. He does his best to ignore them, tries to take notes, mostly fails on both counts. 

He's at the classroom door that evening. 

"Ah, Mikhailov. Here for your detention, I see. Excellent!"

Kennilworthy beckons Sasha into his office. "Do take a seat, young man," he continues, gesturing to a chair. 

Gesturing at a chair is kind of impossible to misinterpret. He sits, looks up at Kennilworthy rather than down at the desk. 

Kennilworthy takes a seat himself, across from Sasha. "Now, I wanted to talk to you about—"

There's a knock at the door. He glares at it, then sighs. "Yes? Who is it?" 

The interruption turns out to be a Ravenclaw girl, who stammers something about Peeves that has Kennilworthy leaping up to follow her. He doubles back after a moment, grabs a DADA textbook, and flips it to a page covering the material they discussed in class that morning.

"I shan't be long," he tells Sasha. "You copy this down—here's paper and ink. Just got to go deal with this; back in a tick." And then he's out of the door.