Note: This takes place immediately after the train flashback scene in the Deathly Hallows chapter, "The Prince's Tale." I figured that if Harry could meet his future best friends on his first journey to Hogwarts, then why not Remus? :)
Sitting alone in a compartment near the end of the train, Remus pressed his face against the window and smiled as he watched the countryside speeding past. He could hardly believe that he was going to Hogwarts. All summer he had half-expected an owl to arrive from Professor Dumbledore, regretfully informing him that he could not, in fact, attend school after all. But no such letter had arrived, and now here he was on a train hurtling towards Hogwarts, against all odds and expectations.
The sound of the compartment door sliding open interrupted Remus' thoughts, and when he turned from the window he discovered two children about his own age standing uncertainly in the doorway.
"Sorry," said a girl with red hair and equally red eyes. It was clear that she had been crying recently. Behind her was a boy with lank hair and a sallow complexion. "Do you mind…?"
"Not at all," Remus replied. He very nearly introduced himself, but remained silent as the girl sat across from him, sniffling wetly and furtively wiping her eyes. The boy sat beside her, ignoring Remus completely and glancing frequently at the girl as if he didn't know what to say.
After a long, puzzled moment, Remus returned his gaze to the window. He felt distinctly uncomfortable with his two new companions. Silence in an empty compartment was one thing, but this was just awkward. He glanced at the girl warily, wondering if she would start crying again, or if perhaps she and the boy would argue. Though neither danger seemed imminent, Remus eventually stood and crept to the door. He thought it would be best if he explored the train for a bit and gave them some time to sort themselves out. After all, Remus reasoned, it hardly seemed possible for anyone to remain unhappy for long with Hogwarts to look forward to.
Neither the boy nor the girl seemed to notice as Remus slipped from the compartment and closed the door quietly behind him. As he walked down the corridor, Remus glanced inside every compartment he passed, finding each one full of rowdy, chattering boys and girls of all ages.
Towards the front of the train he discovered a compartment with just two boys sitting inside, hunched over a quidditch magazine. Remus glimpsed the players flying around in one of the pictures, and he unconsciously leaned inside the open doorway, wanting a better look.
The movement caught the boys' attention, and they immediately leapt out of their seats, tossing the magazine aside and withdrawing their wands as they turned to the door, glaring all the while.
Remus froze. The awkward silence in his previous compartment suddenly seemed far more preferable to the outright hostility in this one. He had nearly made up his mind to make a run for it when both boys suddenly grinned. The one with the messy hair and the glasses slipping down his nose spoke first.
"Oh," he said, lowering his wand. "Sorry about that. We thought it was Snivellus again."
Remus had no idea who or what Snivellus was – judging by its unfortunate name he imagined that it must be something dreadful – and he was rather reluctant to stay and find out. He had just decided to retreat back to the safety of the other compartment when the boy with the slightly longer (but infinitely neater) hair spoke.
"Aren't you coming in? I'm Sirius Black, by the way," he said, sprawling lazily on the seat.
"Those are my chocolate frogs you're sitting on," the other boy grumbled, nearly knocking Sirius to the floor in his haste to rescue them. He glanced over his shoulder at Remus and smiled encouragingly. "I'm James Potter. Here, do you want one?" he said, handing a slightly squashed frog to Remus.
"Thank you," Remus said, feeling a little uncertain around these boys and their lightning-quick moods. He perched on the edge of the seat across from Sirius and James and hesitantly looked from one boy to the other. "I'm Remus Lupin." His eyes once more strayed to the quidditch magazine, now lying carelessly on the floor.
"Do you like quidditch, then?" James asked eagerly. "I wish Hogwarts let first years on the house teams. I'm going to try out as soon as possible, aren't you?"
"No," Remus replied. "I don't play."
"You don't?" James cried, aghast. "But you know how to fly, don't you?"
Remus smiled. "Yes, I like flying very much."
James looked relieved at that. "What house do you think you'll be in?"
Remus' brow furrowed; it was something he had not thought much about. He was so grateful to be going to Hogwarts at all that he hardly cared where they put him.
"Well," he said after some consideration, "my dad was in Gryffindor."
"So was mine," James said, regarding Remus with an all new respect. "I'm hoping for Gryffindor, too. And Sirius here is going to try and break tradition," he added, nudging the boy beside him, who had been curiously studying Remus for several long moments.
"Everyone in my family has always been in Slytherin," Sirius explained. He continued to peer closely at Remus, taking in his faded shirt, his slightly too-short trousers, and his grubby trainers with the frayed laces.
Remus felt a blush beginning to spread across his face and he wished fervently that he had changed into his school robes as soon as he had got on the train. Both Sirius and James were wearing robes – not their school ones, but fine, everyday ones with fancy silver clasps, the kind that Remus had seen other wizards wearing when he visited Diagon Alley to buy his school supplies – and Remus suddenly felt self-conscious of his old, Muggle-style clothes.
But Sirius seemed to be studying him not in disgust, but in fascination. "Is your mum a Muggle?" he asked at last.
"Yes," Remus replied. He wondered if Sirius and James would like him less for having a Muggle mother, and tried very hard to suppress the little voice in his head that cruelly reminded him that if they knew his secret they would certainly dislike him.
"Lucky," Sirius said with a grin. "I've always wanted trainers." He leaned forward suddenly. "Do you think – if we're in the same house, that is – do you think I could borrow them sometime?"
Remus glanced from his filthy trainers to Sirius' shoes, which were clearly new and quite possibly made of dragon hide, and finally to Sirius' eager face. "All right," Remus promised with a smile.
James snickered. "You won't fit into them," he said, leaning over to compare their feet. "Not without enlarging them first."
"That's easy enough," Sirius said, shrugging. "I know lots of charms already. Hexes too."
"Yeah? Like what?"
"Well, there's the Stinging Hex, but that's common enough. And there's one that'll freeze someone's toes off."
"Where did you learn that?" Remus asked, torn between fascination and disgust.
Sirius shifted uncomfortably. "My cousins know a lot of hexes," he mumbled. "I sort of learned from them, I suppose."
"Well, go on," James said. "What else?"
"There's another that'll give someone fangs and claws – are you all right, Remus?"
Remus, who had suddenly gone very pale, began to panic. If he was going to react so strongly to anything remotely related to being a werewolf, people were going to discover the truth in no time at all. "Nothing," he said, forcing himself to smile. "It's nothing. I suppose I was just thinking that it would be rather awful to be hexed."
Sirius smiled in reassurance. "Well," he said reasonably, "we won't hex you."
The rest of the journey passed uneventfully, and it seemed that hardly any time at all had passed before Remus had to hurry back to his compartment and change into his school robes. He lost James and Sirius in the crowd as the train emptied, and ended up sharing a boat with the red-haired girl and sallow-faced boy from before, both of whom seemed to be in better spirits now that the castle loomed before them.
And later, after he had been sorted into Gryffindor along with Sirius and James and a little, mousy-haired boy named Peter Pettigrew, Remus sat with his new acquaintances (he was reluctant to call them friends. He had never had friends before and did not know if that's what these boys were, just yet) during the feast and went with them to the dormitory, talking and laughing all the while.
By the time they finally climbed the steps to their room, Remus was so exhausted that he nearly fell asleep before changing into his pyjamas. But he forced himself to stay awake long enough so that, when the others were settled in their beds and with their curtains drawn, he could tiptoe over to the bed beside his and leave his trainers right where Sirius would find them in the morning.