Peter really, really did not like Hermione's new cat.

The creature—Crookshanks, he was called—was settled against the compartment seat across from Ron and Harry, his yellow eyes fixed intently on Peter every time he dared to poke his head out of Ron's front pocket. Cats tended to go after rats—Peter had certainly had to flee from one or two of them before—but the way Crookshanks looked at him was not animalistic at all. The cat's gaze was piercing and suspicious, as if he somehow knew Peter wasn't what he seemed and hated him for it. He had to be at least part Kneazle; he certainly was big enough to be.

"I still can't believe you chose that…that beast over everything else in the Menagerie," Ron was grumbling to Hermione. "I thought you wanted an owl."

"I couldn't just leave him there," Hermione protested, stroking Crookshanks affectionately. The cat purred in response, but he didn't take his eyes off of Peter. "No one wanted him, Ron, he'd been there for nearly a year…and he's such a handsome thing, aren't you, Crookshanks?"

"He wants to eat my rat," Ron retorted. "He was already ill, and then you went and got that bloody cat, and now look at him—he's in even worse shape!"

Peter very much appreciated Ron's defending him from Crookshanks. Initially he had been none too pleased to be passed off to him a couple years back; Ron was much less diligent than Percy had been, sometimes forgetting to feed him before bed and getting into all sorts of dangerous situations. But secretly Peter had enjoyed his time with Ron and Harry and Hermione, watching them navigate their first two years at Hogwarts as he had once done with his friends so many years ago. Harry was the James of their group, of course, though he was much kinder and softer than James had ever been, and Hermione was as studious and wise as Remus. And Ron…Ron reminded Peter a bit of himself, anxious and underestimated and always overshadowed by his friends, only Ron was ten times braver than Peter could ever hope to be. Ron would never have betrayed his friends to Voldemort.

"Quiet," Harry hissed as Ron and Hermione's argument over Crookshanks escalated in volume. He gestured to the man sleeping against the window, pale and weak and shivering—Remus Lupin, Hogwarts' newest professor, sleeping off the effects of the previous night's full moon. Peter hadn't seen him in twelve years—how could he have?—but his old friend was not looking well at all. His threadbare robes seemed on the verge of tearing apart, and his hair looked like it hadn't been cut in months. Remus's unexpected reappearance in Peter's life—and the fact that Remus knew his rat and knew his secret, even if he didn't believe Peter was still alive—was the second thing that had been making him feel ill throughout the train ride.

But neither Crookshanks nor Remus was the reason Peter could no longer sleep at night, the reason his fur was falling out in clumps and he could barely keep his food down. What scared Peter the most was the news he'd been hearing nonstop for the entirety of the past month: Sirius had escaped from Azkaban, and no one had any idea where to find him. But Peter knew: Sirius would be tracking him down, looking to get his revenge for everything he had done to him. Hogwarts would be harder to break into than ever before, but Sirius would find a way. He always did.

The train thudded to a sudden stop, tearing Peter from his thoughts, and the lanterns overhead flickered out and threw them all into darkness so complete even rat-Peter couldn't see anything. The carriage instantly dissolved into chaos; two more students, the Longbottoms' son and Ron's little sister Ginny, stumbled into their compartment, and then came the hoarse, all-too-familiar voice of a finally-awake Remus as he called for the students to be quiet, summoning a ball of flames into his palm to give them some light. Carefully he approached the compartment door….

And then the door slid open, and the dark, cloaked figure of a Dementor glided into the light of Remus's flames; it hovered silently for a moment, then it took a breath….

The compartment went cold, cold like the bottom of the sea or the far reaches of outer space, and Peter was filled with a terrible, all-consuming hollowness. Beside Ron, Harry slipped from his seat and collapsed onto the floor, convulsing and making awful little moaning sounds. The Dementor was forcing him to relive his worst memories, memories Peter was very much responsible for…. This is your fault, said a voice inside his head. Harry moaned louder. Look how much you hurt that boy. You should be dead, Peter. Sirius will tear your little traitor self apart, and you'll deserve every bit of agony. You deserve nothing but pain.

"None of us is hiding Sirius Black under our cloaks," Remus was saying to the Dementor. "Go."

The Dementor stayed where it was. The voice in Peter's head grew louder—you are worthless, disgusting, a pathetic excuse for a man—until Remus's non-corporeal Patronus burst from the tip of his wand, sending the Dementor retreating back down the aisle. The voice left with it, and the cold, but the hollowness did not.

A minute later and the lights were back on, the train beginning to move once more. Harry was revived by his friends, and Remus calmed the students with pieces of chocolate—Honeydukes', his favorite. Though they were still concerned for Harry, they'd all at least somewhat recovered from the Dementor's appearance by the time the train pulled into Hogsmeade station. Not Peter, though—there was no chocolate or reassurances for him. He shivered and burrowed deep into Ron's pocket; he felt Ron's finger stroking between his ears, trying to comfort him, but it was no use.

Peter had a nasty feeling, festering over the last few weeks and now stronger than ever, that the terrible deeds of his past were finally about to catch up with him.