Robin did not see a lot of the famous Harry Potter in the first few weeks of term, except for when they were in class. After their journey on the Hogwarts Express together, he had taken rather a shining to Hermione Granger, and it appeared that Harry and Ron, who had become firm friends already, found her insufferable. Therefore, their paths rarely crossed. However, Robin didn't particularly mind this. He found Harry rather difficult to talk to, if he was being honest – just a little unnerving, as though he wasn't used to making conversation.

Hermione, on the other hand, had the opposite problem. Where Harry didn't talk enough, she said too much. Robin often found it difficult to find spaces in her word vomit to interrupt with his own opinion. That being said, she was a very capable student, and was very happy to have Robin around. It seemed no one else was too interested in being her friend. Thus, when he needed a favour, he knew she would not hesitate to agree.

So, as they stood up from the breakfast table on Friday and began to make their way to their first ever Potions lesson, he asked lightly, "I was wondering if you could help me with something?"

Hermione, who was walking very quickly in her agitation to get their early and impress the notoriously bad-tempered Professor Snape, replied in a slightly irritated tone. "Oh? What with?"

"Well," he said briskly as they began to descend the stairs to the dungeon, "I'm trying to find out who my father is, and I need help finding him in the school records."

It was surprising enough to make Hermione stop and stare at him. She blinked a few times, mouth wide open, before saying, rather awkwardly, "He… he was a student at Hogwarts, then?"

"According to my mum." Robin found he couldn't quite look Hermione in the eye. He felt as though she might be pitying him, and he couldn't stand the thought. "A Gryffindor. They met through a mutual friend in his dorm. And I thought they must have records of old students in the library – photos, maybe."

She was chewing the inside of her mouth, contemplating. "Do you know his name?"

"No," he said quickly, blushing slightly. "My mum refuses to tell me anything about him. You know as much as I do now."

Hermione looked apprehensive. "I didn't realise there was so much you didn't know about him…"

She trailed off, clearly not sure what to say. Children of happy families rarely did understand the experiences of those who came from broken homes. Robin said, rather fiercely, "But that's about to change. Only it'll change a lot faster if you help me."

For a moment, he thought she might say no. Although his mother wasn't technically a teacher, she was still a member of staff. Robin hadn't known Hermione long, but he was already well aware that she craved the approval of the staff at Hogwarts. To help him would be to directly defy Madame Prewett's wishes. Eventually, however, her loyalty – and desire to engage in some extra-curricular research – kicked in.

"Alright! We can start this evening if you want – I think it just might work, as long as the two of you share a passing resemblance…"

Her mind made up, she spent the rest of their journey to the classroom and the subsequent waiting period outside the door discussing the plan. They would go to the library and start in the school pictures section, looking only at students who had been in Gryffindor house from September 1971 to August 1978. All in all, it would be quite a small number of documents they had to peruse through. The thought made Robin's toes tingle with excitement. After eleven years of strict silence on the matter, he was only a few hours away from finding out who his father was. He was so hyper-focused on this idea, that he barely noticed the other Gryffindors and Slytherins lining up behind them, or even Hermione's continued musings. It wasn't until Professor Snape finally emerged, a towering pillar of black robes, that he looked up in a start.

The whole class, in fact, fell silent. They had not been this quiet since Transfiguration with McGonagall. Snape surveyed them coldly, deep black eyes roaming over their cowed faces, pausing briefly to flick over Robin. They had not met before now, and Robin had the strangest sensation that he was being x-rayed. His gaze was not warm.

"In."

He swept back into the classroom without another word, leaving everyone to file in after him. Hermione headed straight to the desk right in front of Snape, determined to prove herself. Robin couldn't help but inwardly groan. The Potions Master was deeply unsettling, and he would have preferred to be as far away as possible. Still, he also wasn't exactly in the position to abandon her after she had so kindly agreed to help him, so he reluctantly sat down next to her. He couldn't be certain, but he could have sworn that he briefly caught Snape staring at him again. By the time he was able to concentrate fully on the professor, however, Snape's gaze was solidly fixed on the register.

His voice was deep and resonant, but far from comforting as he read through everyone's names. He did not pause at any point until he got to Harry. At this point, he sneered.

"Ah yes," he murmured softly, a curl at the corner of his mouth. "Harry Potter. Our new celebrity."

There were a few titters from the Slytherins, and whispers from the Gryffindors. Robin looked over to where his cousin and Harry were sat, and saw that the latter's face had turned a faint shade of pink. He was just thinking how he would have hated to be singled out like that in front of the whole class when he heard his own name fall off the Potion Master's tongue.

"Prewett, Christopher."

"Oh, um," he said in response, a little meekly, "people usually call me Robin."

He regretted the words as soon as he had left his mouth. Snape, who had already had his fun with Harry, had seemed ready to let Robin's name pass without comment. Now he looked up, between curtains of long black hair, and said coolly and not without a hint of sarcasm, "Fascinating."

Robin wished he could sink into the flagstone floor as the Slytherins all sniggered around him. Snape, it appeared however, wasn't finished.

"I in fact did not recognise your name, Mr Prewett, but it was not your first name that threw me –" Here he paused to shoot Robin a nasty smirk. "– rather the fact that I was expecting to see you further up the register."

The Slytherins tittered again out of habit, but like Robin they seemed to be a little confused. It seemed no one had really grasped the point of Snape's veiled words; no one except Hermione, that is, who was shooting Robin a meaningful look from the other side of the desk which he did not understand. Unsure what to say in response, Robin simply bowed his head, and Snape – seemingly satisfied – carried on where he had left off.

The lesson was quite disastrous. The first ten minutes consisted of Snape partaking in what could only be described as a targeted attack against Harry Potter, where the Professor barraged the poor first year with questions well beyond his skill set and then deducted points from Gryffindor when he failed to answer them. Robin felt sorry for Harry, but elected to stay quiet. When Hermione had volunteered answers in Harry's place, she had succeeded only in making Snape even more vindictive, and as Robin was already seemingly in Snape's bad books, he thought speaking out would only cause more problems. His fears were confirmed when Snape glided over to their desk to put him and Hermione into a pair.

"Time to find out if your mother's potion-making talents were passed down," he said waspishly. His lip curled at the sight of Robin's pale face and shaking hands. "Although somehow I doubt it."

He swept away, leaving Robin even more nervous than before. His mother had tried to teach him how to brew simple potions before, but he had always been uninterested. Now he was wishing he had paid more attention. Thankfully Hermione placed a reassuring hand on his elbow and, with her gently guiding him through all the steps, they managed to make a somewhat decent boil cure.

The same could not be said for everyone, however. Across the dungeons, there was a loud cry as Seamus Finnigan's cauldron melted, covering Neville – the boy with the toad – in a potion that did not look like it was supposed to. Boils began to erupt all over his face immediately, and he wailed. It was like watching a car crash: you couldn't look away.

"Idiot boy!" Snape snapped, as he swept over to their corner. He cleared the potion up in an instant with his wand, but his face was livid. "I suppose you added the porcupine quills before taking the cauldron off the fire?"

Neville just whimpered in response. Snape turned quickly to Robin, and Robin quailed in the line of fire. "Take him to your mother."

Not needing to be told twice, Robin grabbed Neville by his right elbow, the only part of him that wasn't covered in boils, and steered him out into the corridor. As they left the room, Robin heard Snape begin to lay into Harry Potter, but for what reason he didn't quite grasp.

Neville, who could only take small, painful steps, tried to mumble something to Robin, but it was incomprehensible. From the expression in his eyes, however, it seemed that he was attempting to say 'sorry'. Robin shook his head.

"It's okay, we all make mistakes. Just – try not to speak, okay?"

Neville nodded tearfully.

Until that point, Rose's morning had been reasonably uneventful. A Ravenclaw fifth year had managed to give himself a nosebleed during Charms, but that had been a simple counter-spell and the boy was soon back on his way. Once Neville and Robin walked into the hospital wing though, she knew the relaxing portion of her day was about to end.

"Oh my, what happened to you?" she said kindly, as her son led Neville to the nearest bed and sat him down. Neville tried to tell her, but the boils on his lips were too sore, and so he gave up. It was Robin who filled his mother in.

"We were in Potions class, and we were making a cure for boils – I think Professor Snape said he added the porcupine quills too soon…?"

It meant nothing to Robin, but Rose winced in understanding. "Oh dear, yes, that can be quite painful. Luckily," she continued confidently as she hurried over to the medicine cabinet at the back of the infirmary, "I made a balm for just this sort of situation only yesterday…"

Robin gave Neville the thumbs up. "See? Told you it would be fine."

The boy aimed for a watery smile, though it looked more like a grimace. Meanwhile, Rose was returning to the boys with a glass medicine jar filled with some pale white paste. She was also now wearing a pair of dragon-hide gloves that Robin had seen her wearing now and then while teaching at Beauxbatons or when he had hurt himself. She knelt down in front of Neville and began applying the paste to every boil she could see. They began shrinking immediately, leaving only small red blotches.

"Those will go away in a few days," she reassured Neville, who was analysing one spot on the back of his hand worriedly. "What did you two boys think of your first potions lesson?"

The two boys shared a glace that told Rose all she needed to know. Then Robin said, rather timidly, "Professor Snape is quite…"

"Terrifying," piped Neville, who could now speak as Rose had finished treating the boils around his mouth. Robin nodded guiltily, but Rose just laughed.

"Yes, yes, he's certainly not everyone's cup of tea," she said a little darkly, causing her son to shoot her a sharp look that she ignored. Still, as she focused her energies on healing a particularly nasty boil underneath Neville's left eyebrow, she could not help but notice that Robin was chewing his bottom lip, as he always did when he was considering something very carefully.

Finally, he said cautiously, "Professor Snape mentioned something, but we couldn't make sense of it."

"Oh really?" She was trying to seem nonchalant, but there was a definite strain to her voice. "And what was that?"

"He said he expected to see my name further up the register?" He shook his head, revealing his own confusion. "I couldn't work it out. Do you know what he –"

"Professor Snape is not a good man, Robin," said Rose, interrupting him. She was still trying to sound ambivalent, but there was an edge in her tone that was fooling no one. "I don't like to speak ill of my co-workers, but it's true. If I were you, I would ignore him – I've no idea what he means by that, but whatever it is, it will be cruel. Better to forget it."

Robin did not argue with her, but the two boys shared a look again. The look implied that neither one of them fully trusted that response.

After their little discussion, Robin's mother had dismissed him, citing the fact he needed to go back to class. He felt guilty leaving Neville, who was still a little forlorn after a very stressful morning, but knew that pushing Rose on the subject would only make things worse for him. And so, he went back to class, to find the room empty of everyone, even Snape. He checked his watch and realised that potions had ended fifteen minutes ago, which meant he was now free for the rest of the afternoon. Knowing that Hermione was probably in the library already, he headed straight there. Sure enough, she was sat on a table near the back, surrounded by photo albums, her head buried in one with an emerald-green spine. When she caught sight of Robin, she waved him over, and placed the photo album down on the table so that he could see too.

"Come and look at this!" she whispered, pointing to a picture of ten Hogwarts students. It was sepia-toned, revealing its age, which made it difficult to tell what colour the ties beneath their robes were. Thankfully, there was a small cursive script below that read, Graduating Class of Slytherin House, 1978. Underneath that was a list of names, corresponding to the sitters:

Avery, Antonius Mulciber, Credo Rosier, Evan Snape, Severus Wilkes, Jonathan

Dolohov, Yelena Liebowitz, Leah Malfoy, Delilah Prewett, Rosaline Umbridge, Dolores

Robin could only stare. It was his mother alright, front row, two to the right – only she looked incredibly different. Her red curls, which he was so used to seeing tightly pinned into a bun, were loose and cascading down her back. Her round face was full and chubby, dotted with freckles. The gauntness in her cheeks had not yet arrived, nor the wrinkles on her forehead. The only thing he could say that had solidly remained unchanged were her bright brown eyes, looking out at him with a friendly glint. She looked slightly uncomfortable, he noticed, and kept shifting in her chair, staunchly refusing to look at anyone else. He wasn't surprised when he considered the company around her.

To her left was the Malfoy girl, though Robin did not need the label to recognise that. Her platinum blonde hair, hanging over her shoulders in two long braids, meant she had to be a Malfoy, and he could see the resemblance between her and Draco. The Malfoy girl, too, was looking straight ahead, though he noticed her gaze occasionally flicked over to where his mother was sat.

Hers was not the only one. Directly behind his mother stood none other than Snape. It was not hard to recognise him – though he was younger, he had the same curtains of black hair and dark, hostile eyes. He would look down at Rosaline Prewett now and then, with an inscrutable expression on his face. It was not simple hatred – it was something much more complex than that. It made Robin feel faintly uneasy.

"Strange, isn't it?" said Hermione softly, causing Robin to jump nonetheless. "To think they knew each other back then."

"Mmm," replied Robin, scratching his nose awkwardly. He did not want to think about it at all. "Well, this is interesting, but we're looking for my father, not my mother, and he's a Gryffindor."

"I know, I know," said Hermione, "but look closer – at her left hand."

Grudgingly, Robin obliged. If he squinted, he could just make out the shape of a –

"Is that a ring?"

Hermione nodded encouragingly. "Right! An engagement ring, because there's only one not two. And if you look here –"

She flipped back two leaves in the album, coming to rest on an older photograph, of all the same people. The caption underneath this one read, O.W.L. Class of Slytherin House, 1976. He looked down at his mother, and noticed that she was not even pretending to smile in this one. Her face was stony, and she was sat on the edge of her seat, as though she were trying to put as much distance between herself and Snape as possible. Where Snape's expression had been unreadable before, it was clearly furious here. Instead of looking at the camera, he was now unabashedly staring at the back of Prewett's head, as though hoping he might burn a hole through it.

"– here, there is no ring." Hermione tapped on his mother's left hand to prove it. "Now that doesn't tell us a lot, of course, but it proves she wasn't lying about meeting your father at Hogwarts. At some point between July 1976 and July 1978, your mother got engaged."

"Right." He was beginning to get excited again now, as he sat down next to Hermione, making room by pushing her bag aside. "So where do we start looking for him?"

Hermione picked up one of the albums near her. Instead of an emerald-green colour, this one was a bright scarlet. "Here – it's the official Gryffindor photograph album for the twentieth century. When we graduate and pass our O.W.L.s, our photos will go in here too," she mused as she flicked through the pages. "There are two photos for every year, one for fifth years and one for seventh – so if we're looking for 1978, it should be…" She fell quiet, and then slammed the album down triumphantly. "Here!"

There was no mistaking what house the students were in this picture – the scarlet ties shone through the sepia with no problem. The class of 1978 in Gryffindor House looked a much more cheerful bunch, and were labelled as follows:

Black, Sirius Lupin, Remus Pettigrew, Peter Potter, James Shacklebolt, Kingsley

Evans, Lily Macdonald, Mary Mackinnon, Marlene Meadowes, Dorcas Taylor, Emily

"There's no saying that your father attended Hogwarts in that year, Robin," said Hermione warningly. "I would say it's feasible that they could have graduated Hogwarts anywhere from 1975 to 1979. This is just the most obvious place to start."

Robin cocked his head to one side. "And how do you work that out?"

She looked as though she had been waiting on tenterhooks for him to ask. "Well – you said that they met through a mutual friend in his dorm. I think it's very unlikely that your mother would have been friends or in a relationship with anyone who graduated earlier than 1975, because she would have been younger than a fourth year. And you were born in 1980, which means that 1979 is as late as we can go because after that, there was no opportunity for you to be – well –" She looked awkwardly into his blank stare. "You'll just have to trust me on that one."

He did trust her, and he shook his head in awe. "This is insane, Hermione, how you can think of all this stuff."

Hermione looked particularly smug. "And that's not all – we also know that his name has to come before 'Prewett' in the alphabet."

"How do we know that?" asked Robin, a little lost.

"Isn't it obvious?" Robin shook his head again, and Hermione sighed. "Professor Snape said that he was surprised not to see your name earlier in the register, which had to be a dig at your father."

Robin thought about it. The whole thing was starting to make sense, especially given the fact that Professor Snape and his mother clearly didn't like each other. "You're right! But that means –" He looked down at the picture again. "That means any of these men could be my father."

"The only thing we have to go off of is physical appearance, so… do any of them look like you?"

The five young men stared back at him, smiling and laughing. They seemed happy. None of them looked like a man who would abandon his wife and child completely. He would have to look more carefully. He craned his head forward, so that he could get a closer look. It was almost impossible to establish eye colour unless the colour in question was brown or black, though hair colour was slightly more discernible.

"It's not Kingsley Shacklebolt or James Potter," he murmured to himself. Then added, under his breath, "Which is a relief…" He did not think he could have handled the idea of being Harry Potter's brother.

"How did you work that out?"

"I have grey eyes…" he said slowly. "My mum's whole family have brown, so my eyes have to be from my dad. Same goes for hair, they have to have dark hair."

"Who does that leave?"

"Sirius Black."

He paused, analysing the boy closely. He was reasonably tall, with dark hair and light eyes, and strong facial features. He was grinning teasingly at the camera – now and then, one of the other boys would look over at him, and he would wink, causing them all to erupt in laughter. He seemed, to put it frankly, quite cool.

Robin shook his head. "No, it's not him."

Hermione was perplexed. "How do you know? He does look quite like you…"

"Because mum would never go out with someone like that," said Robin firmly. "Trust me. We need to keep looking."

They continued to look for another hour, and came across at least five other boys who fit the description of light eyes and dark hair. At least four of them could have feasibly been Robin's father, with a similar bone structure. There was one boy, a Thomas Harrington who had graduated in 1977, that Robin was quite taken with. He had a calm, thoughtful presence in the photo that reminded Robin very much of himself. Still, it was impossible to say for certain. There was too much conjecture, too much space for misdirection to take hold, and by the end of an hour, Robin had called the search off.

"It's no use," he said glumly. "It's impossible to tell from just these photographs."

Hermione bit her lip sadly, and put a comforting hand on Robin's arm. "Maybe we could come back tomorrow?"

But Robin brushed her hand away. "No, it's fine. It's not that important anyway."

This was far from the truth, but Robin simply could not stand the feeling of disappointment and failure that was settling over him. In all of this regret, the name 'Sirius Black' was forgotten by both of them completely.