He arrived early and exhausted at King's Cross Station on September the first, hoping to secure an empty compartment for himself. He was in no mood for company. The full moon the previous night had drained him utterly, and under normal circumstances, he would have spent the day sleeping and regaining his strength. He hoped he would be able to sleep on the train; the soothing sound of the rails might help, but memories lay thick on the ground here, and he feared the dreams they might inspire.

Boarding the Hogwarts Express apprehensively for the first time in fifteen years, he made his way from car to car. Here was the compartment where James and Sirius had set off a load of dung bombs under the seat of a sleeping Severus Snape. Here, they had played Strip Exploding Snap, and had been caught and reprimanded by the witch with the food trolly. Here, he had walked in on Lily and James having a blazing row. And here - here was the compartment where he had seen Sirius for the first time, over twenty years ago. He hurried past, and at last found a memory-free - and mercifully also student-free - compartment at the end of the train. There, he pulled his cloak up over his head, and went to sleep.

He awoke, disoriented this time not due to disturbing dreams, but because it was suddenly very dark and very cold. The train had stopped and the lights were out, but he could hear children's voices calling to one another, nervously asking what was happening. From the sound of it, there were three or four children in his own compartment now. More entered, tripping over the others and exchanging hurried apologies.

"Quiet!" he told them, quickly lighting his wand. "Stay where you are."

He rose, and was just about to move toward the door, when it opened. Standing in the corridor was the thing he had known it must be, but had hoped it was not: a Dementor of Azkaban.

The temperature in the compartment dropped still further as the tall, black-clad creature drew a rattling breath. By the dim light of his wand, Remus saw a boy drop into a dead faint. The other children were clearly terrified, cowering back against the seats. Remus did not feel much braver than they looked, but as their Defence Against the Dark Arts teacher, and as the only adult present, he knew he must do something.

His mind filled with the image of Sirius laughing madly, surrounded by the death and destruction he had wrought.

Oh, no you don't! he thought. That image was with him daily; the Dementors could not break what was already broken.

He stepped over the prostrate form of the fallen boy, looked the Dementor squarely in what he supposed must be its face and said, "None of us is hiding Sirius Black under our cloaks. Go." His heart skipped a beat and his mouth went dry as he spoke the name he had not voluntarily uttered in twelve years.

The Dementor did not move. If it did not understand his words, still he knew one thing to which it would respond.

"Expecto Patronum," he muttered softly, trying his hardest to summon up a happy thought.

It was a pathetically weak Patronus - barely more than a flash of silver light - but the Dementor turned and quickly retreated down the corridor, taking some of the cold with it.

For a moment, there was silence in the compartment. He could feel all the children's eyes on him. Then the train shuddered back to life, the lights came back on, and the Hogwarts Express began to move again.

"Harry!" cried a girl, crouching beside the prone form on the floor. "Harry! Are you all right? Wake up!" The other children crowded around the unconscious boy.

Remus stared, stunned, at the boy's face, but there could be no mistaking him. Even without the telltale mark on his forehead, he looked enough like James to make Remus feel mildly dizzy. So this was the boy he had been living for. Then Harry's eyes opened, and Remus felt a second painful lurch at the colour - a deep, emerald green, just like Lily's.

The other children crowded in, asking the boy if he was all right. He looked very pale. None of them paid the slightest attention to Remus, giving him a much-needed chance to recover himself. Harry asked whether anyone had heard screaming, but Remus could not remember anyone having screamed.

He shook himself. Chocolate. That was what was needed under the circumstances. Remus took a large slab of the stuff from his bag, and broke off a piece for Harry.

"Here," he said hoarsely. "Eat it. It will help."

Everyone was looking at him again. He began handing out smaller bits of chocolate to the other children, as he explained to them what they had just seen.

"I need to speak to the driver," he lied then, and left the compartment quickly.

What he really needed was time alone to collect himself. There had been no mistaking James's son, nor Lily's either. It was as if their ghosts had walked into that compartment and spoken to Remus. Well, in a way, they had. He had a duty to them; he must protect their son. With that thought firmly in mind, he went to send an owl ahead to Dumbledore.

Remus's reintroduction to his old school continued to be both disconcerting and bewildering. In a way, it felt like coming home. Not only was he amidst familiar surroundings, but he was properly a part of the Wizarding world again for the first time in more than a decade. He had lived for so long as an outsider - almost a ghost - that just hearing all these young voices and being surrounded by so many people felt strange.

The children looked upon him with either speculation, or outright mistrust. They all surely knew which post he had come to fill, and Dumbledore's letter had informed him that their previous experience of Defence Against the Dark Arts masters had been less than confidence-inspiring. It was understandable that they would view a newcomer with suspicion.

In another way, coming back to this place made him feel more like a ghost than ever. He was still an outsider. When last he had walked these halls, they had been filled with friendly - or at least familiar - faces. These children were strangers to him. Some of the professors he knew, and some he would rather he didn't, but all in all, coming back was a very lonely feeling.

He drifted into the Great Hall, and found his place at the head table among the other professors. Headmaster Dumbledore offered him a warm greeting, looking very much as he had in Remus's own schooldays: a tall, cheerful man with twinkling eyes, of indeterminate but decidedly great age.

And then there was Severus Snape. It had been many years since Remus had seen him, but he looked just as Remus would have expected him to look by now: bitter, sour, unwashed, and beginning to age ungracefully. The black-haired professor met his eyes for an instant, but they both looked away quickly in dislike. Remus had been warned that the man was Potions master here. In fact, it was Snape who would be making the new Wolfsbane potion for him when the full moon approached. Neither man was happy with this arrangement, but it was a necessary one; Remus had always been woefully unskilled when it came to potions.

Remus's feeling of otherness was not to last long, however. His isolation from his surroundings crumbled a little when Dumbledore - old, familiar, warm, funny Albus Dumbledore - rose to make the start-of-term announcements. These began, of course, with the bad news about the presence of the Dementors around the school grounds, and their search for Sirius, but since these thoughts were never far from Remus's mind, they caused him no undue discomfort.

When Dumbledore announced his own arrival, the halfhearted applause of the students was broken by enthusiastic cheers and whistles from the middle of the Gryffindor table. Remus looked in surprise, and saw Harry and his friends beaming down the table at him. At once, the feel of the place changed. These children - and especially that child - were glad he had come to Hogwarts, and suddenly, so was he.

This feeling of tentative optimism was nearly lost to him, following the banquet. He was prowling the corridors in a much better frame of mind than when he had first arrived, remembering the happy and innocent moments of his early days at Hogwarts, helped along in these thoughts by the clusters of first years, discovering the wonders of the castle for the first time.

Then he turned down a corridor, deserted but for one person: Severus Snape.

"Lupin," Snape said, nodding stiffly. A twitch of his lip betrayed his barely-concealed dislike.

Remus sighed. He knew this could only go one of two ways: either they could spend the rest of the year pretending not to know one another and avoiding all contact, or they could acknowledge their long-standing animosity, and try to deal with it like the adults they now were.

"Severus," he said, steeling himself. "You're looking -" But he could not think of anything complimentary, or even civil, with which to end the greeting.

"Indeed," replied the Potions master with a chilly smile. "As are you."

His eyes traveled over Remus, taking in his shabby appearance, the lines of hardship and old grief etched into his face, and the premature graying of his hair.

"Severus -"

But Snape cut him off with a hiss. "Never forget, Lupin; I know what you are. I know what you've done. And yes, I know who you've fucked, as well. Dumbledore may trust you, but that old man can be a sentimental fool. I know you. Make no mistake; I saw enough during our schooldays, and heard enough after, to know that you're a man to be watched, especially now that the name of Sirius Black is being whispered again. I'll make your damnable potion, because someone has to for the sake of this school, but know this: I will have my eye on you." And with that, he turned on his heel and strode away down the darkened corridor, robes billowing in his wake.

Remus closed his eyes and sighed. Apparently schoolboy grudges were not to be forgotten, at least not while the two of them were still within the walls of Hogwarts. It was going to be a long year.