Like Harry, many others were trapped in terrifying memories.
The Hogwarts Express was under attack by countless Dementors.
They broke through the doors and swarmed inside without permission, plunging the entire train into a cold wave that left countless first-years shivering.
That wasn't the worst of it.
A few Dementors even drew close to the students, sucking away their happiness and plunging them into even deeper terror.
"Expecto Patronum!"
The plainly dressed professor standing before Harry suddenly cried out.
Silver mist rose from his wand, with faint silver glimmers flickering deep within it.
The Dementor seemed frightened. It began to retreat, trying to leave the compartment.
But by then, Harry's pain had eased.
He raised his wand and used the same spell.
Only, the silver mist bursting from Harry's wand was far smaller than the professor's.
Even so, Harry bravely held up his wand and charged out.
"Come back, Harry!"
Professor Lupin called out anxiously, but Harry looked like he'd gone mad.
He charged forward without a care, his wand spitting silver mist with a crackling hiss, like a firework with its fuse lit.
"Harry!"
Ron shouted too, but he couldn't stop the brave Harry either.
He stamped his foot in frustration, then hurried after Harry out of the compartment.
Lupin followed without hesitation, though his steps remained steady and unhurried.
Only after leaving the compartment did he realize the train corridor was filled with silver mist, making it nearly impossible to see more than three meters ahead.
Fortunately, Harry and Ron hadn't gone far. They were jumping down from the train one after the other, chasing the fleeing Dementor.
Lupin glanced down the corridor in confusion, then turned to look toward the place where Harry and Ron had disappeared.
In the end, he set aside his curiosity and followed