Disclaimer: I'm making no profit from this, and no copyright infringement or anything is intended. Most of the dialouge is from chapter 5 of PoA, and full credit goes to the incredible JK Rowling.
A/n: What if Remus was awake the whole time on the Hogwarts Express? (Did you really think he was sleeping, and just popped awake just in time to save them from the dementor?) What were his thoughts through the whole "Sirius Black" discussion? If this seems a little back-and-forth it's supposed to be. Remus is extremely tired, and everything is a haze for him at the moment.
It was the day after the full moon. Remus Lupin doggedly heaved his tattered and patched trunk, which looked about as worn as he, himself, did, above his seat and collapsed onto the bench. "I'd rather avoid this." he said to no one in particular. "The boy's been through enough. He doesn't need me around digging up his past. I swear if Dumbledore wasn't desperate to fill this position..." Before Remus could finish his thought, he had drifted off into an uneasy sleep. That is, until the sound of the compartment door sliding open caught his attention. He kept his eyes close and breathing even, a trick he had learned on his missions for the Order. There was no reason to disturb his visitors if they were in search of a compartment, but Remus was exhausted, and he wasn't about to move.
"Who d'you reckon he is?" he heard a young boy say.
"Professor R.J. Lupin." and girl responded matter-of-factly in a low whisper.
'How did she know that?'
"How d'you know that?" The boy again.
"It's on his case." Clever girl, that. Remus listened as Clever Girl explained to Oblivious to the Obvious Boy that he, Remus, must be the new Defense teacher, and as the boy commented on Remus's tattered state.
'One good hex could finish me off, my arse. I've been through more than you know, son.' Remus thought to himself. The children's conversation was wearing on him, and he began to fall asleep. Remus vaguely heard a different boy speak, but it wasn't until the name Sirius Black came up that he was fully alert once more. What did this boy have to say about Sirius? Remus pushed away the familiar plunge of his stomach at the mention of the name and listened to the conversation again.
"...Sirius Black. That's right. I heard your mum and dad talking, Ron."
'Mental note: Oblivious Boy equals Ron.' Remus cursed his lycanthropy as his body could no longer keep awake. The full moon always left him fatigued.
The next Remus remembered the girl was speaking again, "Sirius Black escaped to come after you? Oh, Harry..."
'Harry? Wait a minute...'
"You'll have to be really, really careful. Don't go looking for trouble, Harry-"
'It couldn't be him. Could it?'
"I don't go looking for trouble. Trouble usually finds me." At this Remus's stomach gave an uneasy lurch. He risked opening his eye slightly. The instant he saw the black mop of hair he knew he was sitting beside James's son.
"How thick would he have to be, to go looking for a nutter who wants to kill him?" Ron said. If he only knew. Remus was drowning in his thoughts; the ruins of Godric's Hollow, Sirius's maniacal laughter as the Azkaban guards hauled him away... When he finally left his memory-induced stupor, he found the conversation had shifted to a more pleasant topic: Hogsmeade. Unwanted memories flooding his head, Remus slipped in and out of consciousness.
"Get out of here!"
"Ron, don't!" An argument had broken out. About what, Remus didn't know, but he thought it best to put a stop to it. He shifted in his sleep and turned his head. This seemed to quell the situation, as the voices in the compartment became hushed once more.
Remus distantly heard the food trolley being pushed. "Er - Professor? Excuse me - Professor?" Leave me alone, Clever Girl, I'm not hungry. Food couldn't possibly solve my problems.
"I suppose he is asleep? I mean - he hasn't died has he?" At this Remus couldn't contain himself, and let out a huff of laughter. All three children jumped in alarm.
"No, no, he's breathing."
Remus decided to take a real nap for a bit. He would talk to Harry at school in private. The kids needed some privacy on their trip. How well he remembered riding the Hogwarts Express every year with the Marauders, and how James and Sirius had enjoyed themselves planning pranks for the upcoming year, while Peter listened, captivated, and he, Remus, sat quietly, thinking of ways to not get expelled thanks to James and Sirius's plans.
The train began to slow. 'We couldn't have arrived already?' Remus thought. A sudden jolt told them they had stopped completely, and the next second all the lights had flickered off. 'Something's not right here.' Remus sat up now, his wand at the ready. He could hear Harry, Ron, and the girl (who, by listening to the idol chit-chat in the compartment, he found out was named Hermione) were all bustling anxiously about.
Ron looked out of the window and said, "There's something moving out there. I think people are coming aboard..." The party was joined by another boy; Harry had called him Neville.
"I'm going to go ask the driver what's going on," said Hermione. But as she opened the door another girl entered. Not being able to see, they collided with a loud thud. This wasn't was Remus was focused on, however. Their fumbling sounds fell on deaf ears ("Ginny?" "Hermione?" "What are you doing?" "I was looking for Ron -" "Come in and sit down-" "Not here! I'm here!" "Ouch!") as Remus felt an overwhelming cold spread through his body. Only one thing felt like that... It was getting close.
"Quiet!" he said to the still-moving students. They ceased their chatter at once, most likely out of the shock of hearing Remus awake. He performed a simple portable fire spell and held the flickering bundle at arm's length. He took a cursory glance around the compartment and saw a round-face boy, who must have been Neville, twisted awkwardly in his seat and being untangled by the two girls, Ginny and Hermione. Harry Potter (Remus had no doubt now who he was), was sitting rigid and tense, and a red-head boy that must have been Ron looked petrified. "Stay where you are," Remus whispered. As he inched towards the door it began to open slowly. The cold became deeper, filling him. Those painful images rushed through his head once again; Harry as a baby, Lily and James, their promising lives cut tragically short, Godric's Hollow in flames, Peter, tiny Peter, running from Sirius, Sirius laughing...laughing...
Remus wrenched himself from the memories and spoke, "None of us is hiding Sirius Black under our cloaks. Go!" When the dementor showed no sign of moving, Remus dug through his thoughts, looking for something, anything happy. He though of Hogwarts and the Marauders, thought of the adventures they shared and with a touch of sadness in his ragged voice said, "Expecto patronum."
'This is going to be a long year.'