Author's Note: I came up with the idea for this story in 2008, but I never finished it. I felt it was high time to give it another chance!

Mercury Lies
prologue

Professor McGonagall's expression was one of careful amusement, and quite suddenly, the boy sat across from her doubted his decision. 'I'm not sure, however, that I would be the right person for the job,' he attempted.

McGonagall raised only an eyebrow, and pursed her lips in what seemed like disapproval, a look he had never seen aimed at himself before. 'Nonsense,' she told him, taking a sip of her hot tea, the steam of which circled up past her cheek and disappeared into thin air. 'You are one of the brightest students in this school, and I truly doubt that you are as awful at teaching as you wish to make yourself out to be, Mr Lupin.'

Carefully knotting his hands together under the table, sixteen-year-old Remus Lupin, his light brown hair neatly combed, falling just below his ears, and his silver and blue tie, although perhaps not the newest around, knotted perfectly, chalked it up as a losing battle and offered her a smile. 'Of course, Professor,' he said, and finished the rest of his tea.

The next morning, Remus Lupin could be found in bathroom of the Ravenclaw boys dormitory, which he shared with three other students. He was currently trying, for the fifth time, to properly knot his tie, a task he kept failing at because his hands would not stop shaking. The sky outside revealed a dark, thundery October morning, and Remus was the first up, as he always was.

'You are going to be fine,' he told his reflection, which stared back at him through large, round blue eyes.

'Sure you are, dear,' the mirror responded sleepily.

Remus ignored her, and, while clenching his fingers too tightly in the fabric, still managed to knot his tie properly. He nodded once, firmly, at his own reflection, and then pinned on his Prefect badge, before leaving the dormitory quietly, careful not to wake anyone. As he made his way down to the Great Hall for breakfast, he gave some consideration to what had happened yesterday.

After class, Professor McGonagall, who taught Transfiguration, had caught him just as he was about to leave. She invited Remus into her office, and asked him as she poured him some tea into a dainty, floral china cup that seemed completely out of place in her office, if he had every considered becoming a tutor.

'Er, no, Professor, I can't say I have,' he responded, surprised, pulling the book bag that had once belonged to his father a bit closer to his body.

'Take a biscuit, Mr Lupin,' McGonagall said, handing him a cup. Remus blinked, and then remembered his manners. He carefully put his bag on the floor and took it from her, hoping that having something to hold and stir would make him less nervous about this.

'I think you should consider becoming a tutor,' she said, pouring her own tea, and offering him a biscuit from a plate. Remus thought it polite to refuse, so he accepted, holding it up in the air. 'I have discussed it with Professor Flitwick, your Head of House, and we are both convinced you would be most excellent at it.'

'What – what would I need to do?' Remus asked.

'It's nothing too big,' McGonagall replied, her tone business-like. Remus wondered why it seemed to be tinged with a slight tone of annoyance, and then wondered if that was, perhaps, aimed at him. He took a bite out of the biscuit, just to be sure. 'One of my fifth year students, Mr Pettigrew, has not yet caught up with all of his classmates and with his OWLs coming up, I am getting worried. He is a bright boy, but he can be a bit slow on the uptake, and I fear I lack the time to teach him myself.'

Remus felt a slight, uneasy jolt in the pit of his stomach. Peter Pettigrew was good friends with the two other boys in his year in Gryffindor, Sirius Black and James Potter, and the three of them often caused a lot of trouble. Remus didn't know any of them personally – they were in another House and a year below him – but he knew of them, like most everyone in the school did. He really didn't think this would be such a good idea.

As if reading his mind, McGonagall smiled. 'I think you should give it a go, Mr Lupin. If you find it is not for you, there will be no harm done, and I will not ask again.'

'Right,' Remus replied.

'Excellent,' McGonagall said. 'I propose you meet with Mr Pettigrew in the library. If he asks any questions you do not know the answer to, you can always send him to me. How does Friday at eight o'clock in the morning work for you?'

And that was the reason why, on the one day he had no morning classes, Remus was on his way down to breakfast. He was early, as was his habit, and he had a quiet breakfast, during which he finished reading a book for Advanced Charms that was due to be read next week. At promptly half seven, he was in Transfiguration section of the library, tapping his quill against the parchment. To kill some time, he was re-reading an essay that was due the next day, to see if he had made any mistakes. When he glanced at his watch for what felt like the hundredth time, he wondered if Pettigrew was going to show at all.

He sighed, and then, suddenly, he remembered vividly his mother, on the day his parents had taken him to Kings Cross Station to start his very first year at Hogwarts. Her face had been pale, tinged with worry, because the full moon had been just two days ago. Remus, himself, was tired and boasted a new, intricate scar across his neck, which was angry and red and only just barely peeking out of the collar of his robes. She had pulled him towards her, ignoring his faint yelp of protest, and he could smell the sickening smell of worry coming through her thin summer dress.

'Sweetheart,' she had whispered, so softly Remus had had to lean closer to hear. 'Remember to be careful. You have a valuable secret to keep. Do not give it away to anyone. Promise me.' She had clutched his robes, which had felt thick and heavy and suffocating, all of a sudden. It had sounded like a warning.

At that moment, all Remus had been able to think of was the sound of his mother's crying as the only grandparent he had ever known – his grandfather John, strong and Welsh and proud, who had been Remus's favourite person in the world – yelled at her. 'You had to marry a wizard, hadn't you? This is all your fault! I don't ever want to see any of you ever again!' His grandfather had stormed out, then, past a horrified Remus, who had come downstairs to get breakfast. As far as he knew, his parents had never spoken of this moment to anyone, but they had moved out of Chepstow the next day. It was the last time he had ever seen his grandfather.

Back at the station, Remus had felt his mother tense up. He then bit down on his lip until he felt it bleed, and then he had responded, 'I promise, Mum.'

'Thank you,' she had said, her voice thick with tears, which were gone the moment Remus pulled away from her.

This very promise, made when he was just eleven, was the reason Remus kept mostly to himself. He spoke up in class when he knew the answer, he was cordial to his fellow students, and he had a handful of acquaintances he spoke to and studied with occasionally. But he couldn't really say that he had a lot of friends, if any at all. But, he thought to himself, it wasn't like he minded. He knew what people called him behind his back. Loony Lupin.

At precisely a quarter past eight, Peter Pettigrew arrived at his table, bringing along James Potter. 'So sorry I'm late!' Peter half-shouted, upsetting Madame Pince, who glared at him with beady eyes.

'That's all right,' Remus responded, and then made eye-contact with James Potter, who was wearing a bright grin. 'I don't think you're here to be tutored as well?'

'Fuck no,' Potter laughed. Madam Pince made a loud shushing noise, which he ignored. 'I'm just here to drop Petey off, because he's a big girl and didn't want to go by himself. So I escorted him, because I am an excellent friend and Sirius couldn't be bothered to get up this early.'

Pettigrew made a noise of protest at being called a girl, but Potter heartily clapped him on the shoulder. 'See you in Potions!' He gave a dramatic wave and disappeared between the Charms and Muggle Studies aisles closest to them, his footsteps eerily quiet.

Remus looked back at Pettigrew, who was fiddling with the hem of his robes and was avoiding looking at him. 'Why don't you have a seat,' Remus said kindly, and Pettigrew did just that. He looked at the table, and heaved a heavy sigh.

'I'm so sorry you have to put up with me, I'm hopeless at Transfig and I'm terrified that I'm not going to pass my OWL! It's likely my mum will eventually keep her promise and disown me.'

Remus blinked, wondering if all Gryffindors were as dramatic as the two he had just met. Pettigrew still wasn't looking at him, absently scratching his name into the top of the table with his wand. Remus realised he probably needed a bit of reassuring. 'You'll be fine, Pettigrew. OWLs are months away and Professor McGonagall told me you're very bright, so I'm sure you'll be well rid of me in a couple of weeks.'

Pettigrew looked up, beaming. Together, they got to work.

McGonagall hadn't been wrong. Over the next couple of weeks, Pettigrew showed himself to be a clever student, who grasped the theory behind animal to object transfiguration quite quickly. When it came to putting theory into practice, however, he showed little progress, despite the six lessons they'd had so far.

'I give up,' Pettigrew moaned, putting his head in his hands, his wand hanging limply from his fingers. The matchbox he had been trying to transfigure was lying placidly in the same spot Remus had put it ten minutes ago. He had been trying to alter its molecular structure so that it resembled a hamster, but other than the box turning an off-beige colour, nothing had really changed.

'Why don't you try again?' Remus prompted, moving the matchbox towards Pettigrew with his hand. 'I think it's your wand movement.'

Pettigrew raised his head and threw a resentful look at the matchbox, but did as he was told. He swished his wand perfectly but then, as he moved his wrist into the follow-up circle, his fingers overbalanced, just the slightest hint. He didn't seem to notice, finishing with a flourish, and tapping the matchbox. It vibrated, slightly, but otherwise remained unchanged.

Remus looked apologetically up at Pettigrew. 'You're doing it again.'

'Oh, bollocks,' Pettigrew said, hitting the desk with his fist in frustration.

'Don't worry about it, it's a tricky movement. I do think you've had enough for tonight,' Remus said. He cleared away his books, filing them neatly into his bag in alphabetical order, and looked up to find that Pettigrew was holding out the matchbox and the notes Remus had written for him.

'You can keep those,' Remus said. 'For practice.'

'You're joking?' Pettigrew wondered. 'This must've taken you hours!' He gestured at the expansive notes Remus had taken for him, written neatly and covered in charts and diagrams.

'I made them for you,' Remus said firmly, standing up. He got up off his seat and slung his book bag over his shoulder. 'I'll see you next week, Pettigrew.'

'Cheers!' Pettigrew shouted after him.

'Shit,' Peter declared to no one in particular, when he walked into the Gryffindor dormitory that evening, tossing his bag onto his messy bed.

'Who, Lupin?' James asked, although he didn't sound too interested in hearing the answer. He was lying back on his bed, reading Quidditch Weekly, and hadn't even looked up when Peter entered. Sirius, who was lying on the bed next to James, had pretended to have not heard Peter, like he always did. He was tossing a Snitch up in the air, catching it with his other hand. Occasionally, he would toss it to James, who would catch it without looking up, and would throw it back.

'I'm stupid,' Peter announced, flopping down onto the bed, tugging at his Gryffindor tie. When neither of them responded to that, he added, 'Lupin's nice, for, you know, a Ravenclaw. He wrote me notes.'

Sirius snorted. James stared.

'For practice!' Peter said, hotly, wondering how they always managed to make him feel like a complete idiot.

Sirius sniggered.

'I'm going to bed,' Peter announced shortly.