The next morning, the Ministry cars took them to King's Cross station, cutting it close to the departure time for the Hogwarts Express. The students rushed to board the train, pausing just long enough for Mrs Weasley's traditional round of hugs.
In the midst of the commotion, Mr Weasley pulled Harry aside for a quick warning against seeking out Sirius Black. Harry had no idea why the man thought he would ever do such a thing, but the train was about to leave, and he didn't have time to ask for an explanation.
Boarding as late as they had, it took some time to find a compartment that wasn't packed. They settled on one already occupied by a man in a shabby set of robes, who appeared to be sound asleep. None of them recognized him, so they concluded he must be the new Defense Against the Dark Arts teacher–R.J. Lupin, according to the name on his bag.
The teacher's presence turned out to be a useful deterrent against annoyances. When Malfoy and company stopped by for their usual taunting, Ginny gave them a cheerful greeting of, "Hey, guys. Here to make a good first impression on your new teacher?"
This sent them sullenly on their way.
After they settled in for the journey, Harry related Mr Weasley's warning about Sirius Black.
Ron and Hermione were as confused as he was, but Ginny said, "Mum and dad have been talking about him a lot since we got back from Egypt."
Ron said, "I haven't heard anything about it."
"You don't listen as well as I do."
"I don't eavesdrop as well, you mean."
"I can't help it if I have a talent for being in the right place at the right time without getting noticed."
Harry told them what he'd learned about Black from the Knight Bus conductor's newspaper. When he finished, the four friends looked at each other with uneasy expressions.
"How are we going to take him down?" Ginny asked.
"You're not getting involved," Ron told her. "You shouldn't even be hearing this."
Hermione said, "None of us are getting involved. Your father was right to warn Harry away. You aren't thinking of going after him, are you?"
"Of course not," Harry said. "I just wish someone would tell Black not to come after me."
"You don't know that he is. Mr Weasley must have run out of time to explain properly. Sirius Black would have to be crazy to come to Hogwarts with Dumbledore there."
Harry said, "According to the paper, he might be that crazy."
Ron said, "Maybe he'll decide to swing round yours instead, and sort out your relatives while he's there."
"Ron!" Hermione objected.
Ginny said, "I don't think we can count on Hogwarts to be safe, even with Dumbledore. He's not always there when you need him. Look at the last two years. Sooner or later, something bad–Hey, is the train slowing down?"
They all looked out the window at the rain-soaked countryside. The train in fact was slowing down, and soon came to a full stop. The lights went out.
"Like I was saying," Ginny remarked, drawing her wand. "Guess it was sooner."
"There must be a good reason why we've stopped," Hermione said, trying to convince herself as much as her friends.
"Having our wands ready won't cause any harm if nothing happens," Ginny told her.
Harry drew his wand. "It's starting early this year. Usually things don't get insanely dangerous until around Halloween."
Ron and Hermione drew their wands as well.
The door to the compartment opened. Neville Longbottom started to enter, only to freeze and stare wide-eyed at the four wands pointed at him.
They lowered their wands, and Neville asked, "Um. Does anyone know why the train stopped?"
Harry said, "No idea. Come in and close the door."
"And draw your wand," Ginny added.
Neville did as instructed, then sat down.
"Do you think we should wake him?" asked Hermione, gesturing to the sleeping teacher sharing their car.
Ginny asked, "Since when does a Hogwarts Defense teacher actually solve problems, rather than create them?"
"He's still a teacher," Hermione argued. "We shouldn't judge him based on the two people who happened to have the same job right before him."
"The problem with Defense teachers goes back a lot further than two years," Ginny said.
"What do you mean?"
Before she could answer, Harry asked "Is it getting colder?"
Ginny said, "You know I can't feel–" Her eyes went wide. "No, you're right. I actually feel cold. That hasn't happened since–" She broke off, remembering Neville's presence.
"Who's screaming?" Harry asked.
"I don't hear anything," Hermione said.
Harry looked at the others, who shook their heads.
"There's a woman screaming. You have to hear that." He brought his hands up to cover his ears, but this seemed to bring him no relief.
Ginny said, "Wait, I do hear something. It's not a woman screaming. It's a man laughing." She jumped to her feet. "It's him! Riddle is on the train!"
Just then, the door was thrown open. An impossibly tall figure in a hooded robe bent forward to fit through the doorway. The temperature dropped like a stone.
Hermione, Ron and Ginny began casting every jinx and hex they knew. Neville tried to cast at the figure as well, though his spells all fizzled out.
Harry tried to aim his wand, but collapsed to the floor, clutching his head.
The tall figure leaned forward, reaching for him.
"Incendio Maxima!" cast Ginny, sending a torrent of fire into the dark figure's hood. This at last halted its advance, though failed to drive it away. When her spell ended, the figure's hood had been blown back. It turned its face towards her.
It wouldn't be accurate to say the creature looked at her, as its eye sockets were empty and covered over with the same wet, scabby skin as the rest of its face. Its robe smoldered from Ginny's fire, but none of their other spells had affected it in the least.
The gaping hole it had in place of a mouth started to dilate even wider, as the figure once again began to move towards Harry.
"Expecto Patronum!" came a voice from behind them, and a burst of silvery glowing mist drove the thing out of the compartment. Their new Defense teacher stepped forward, driving the horrid thing away.
Ginny dropped to her knees next to Harry and began shaking him. "Harry!" she cried, as the compartment started to warm up again.
Harry's eyes snapped open. He swept his gaze around the compartment. "What happened?"
"That thing came in, and you passed out," she told him. She looked up at the Defense teacher. "And Voldemort is on the train! I heard him!"
The teacher gave her a sympathetic look, but shook his head. "Merely a bad memory, one of the effects produced by entities of that ilk."
"Professor, what was that thing?" Hermione asked.
Ginny demanded to know, "How do I kill it?"
Lupin glanced at them both, but his eyes seemed drawn back to Harry. This was not lost on Ginny, who kept her wand ready while Harry was down.
"Let's all stop to take a breath," Lupin said, "First off, as you have already guessed, I will in fact be one of your teachers this year, in Defense Against the Dark Arts. You may call me Professor Lupin."
The students introduced themselves while Lupin helped Harry up, and gave them all pieces of chocolate. He explained, "That creature was a Dementor, one of the guards of Azkaban Prison. We will be studying them in class this year, among other topics. Chocolate helps remedy the effects of exposure to them."
Ginny felt a pang of guilt. Hagrid had been subjected to those things, because of her.
"Professor," Harry asked, "Why was I the only one that, uh…"
"No need to feel embarrassed, Harry. Dementors cause a range of reactions in different people, none of them pleasant."
"No one can say anything about Harry's reaction," Ginny said, looking around at everyone in the car. "His enemies don't need to know anything they might be able to exploit."
"I'd rather not have anyone know," Harry added. "Enemies or otherwise."
Ginny rested her hand on Harry's arm, but turned to look at Lupin. "You didn't answer my question."
He studied her for a long moment. "I'm afraid there is no known method for killing a Dementor, though one may drive them away with the Patronus Charm, the method you saw me use. Other spells will only provoke them, which becomes even more dangerous if you are dealing with more than one. If you encounter any at Hogwarts, do not engage them. Run and find a teacher. I don't know what the Ministry was thinking, turning one loose on the train."
"I need to learn the Patronus Charm," she told him.
"Me, too," Harry added.
"The spell is extraordinarily complex. Many adults are unable to master it."
They both stared back at him with stubborn expressions.
Lupin sighed. "I will consider it. For now, I must speak to the driver about getting the train moving again." With that, he stepped out of the compartment.
None of them were in the mood for much conversation for the rest of the train ride.
Once getting off at Hogsmeade station though, they started to cheer up at the prospect of returning to Hogwarts.
When they reached the castle, Professor McGonagall was waiting to speak to Hermione about her schedule. She said nothing to Harry about the train, so it seemed Lupin had respected Harry's request for privacy.
Hermione missed the Sorting Ceremony, but managed to arrive in time to hear the headmaster's dire warnings about Dementors, along with his more cheerful announcements about Professor Lupin's appointment to the Defense position, and Hagrid's new job as the Care of Magical Creatures teacher. Harry and his friends applauded politely for Lupin, and were enthusiastic in their cheers for Hagrid.
Hermione looked around the Great Hall. "It's awful that the new first-years have to deal with those dreadful creatures. As if starting at a new school isn't hard enough, wondering if you'll make any friends, learning to find your way around… after getting through the first night of course."
Harry asked, "Where would they need to go on the first night?"
"Nowhere. I meant getting settled in and, you know, homesickness."
Harry blinked at this, as the notion had never occurred to him. He could see his friends all looked somewhat melancholy though, so he kept his thoughts to himself.