But the door slid slowly open before Lupin could reach it.
Standing in the doorway, illuminated by the shivering flames in Lupin’s hand, was a cloaked figure that towered to the ceiling. Its face was completely hidden beneath its hood. Harry’s eyes darted downward, and what he saw made his stomach contract. There was a hand protruding from the cloak and it was glistening, grayish, slimy looking, and scabbed, like something dead that had decayed in water…
But it was visible only for a split second. As though the creature beneath the cloak sensed Harry’s gaze, the hand was suddenly withdrawn into the folds of its black cloak.
And then the thing beneath the hood, whatever it was, drew a long, slow, rattling breath, as though it were trying to suck something more than air from its surroundings.
An intense cold swept over them all. Harry felt his own breath catch in his chest. The cold went deeper than his skin. It was inside his chest, it was inside his very heart…
Harry’s eyes rolled up into his head. He couldn’t see. He was drowning in cold. There was a rushing in his ears as though of water. He was being dragged downward, the roaring growing louder…
And then, from far away, he heard screaming, terrible, terrified, pleading screams. He wanted to help whoever it was, he tried to move his arms, but couldn’t… a thick white fog was swirling around him, inside him—
“Harry! Harry! Are you all right?”
Someone was slapping his face.
“W-what?”
Harry opened his eyes; there were lanterns above him, and the floor was shaking—the Hogwarts Express was moving again and the lights had come back on. He seemed to have slid out of his seat onto the floor. Ron and Hermione were kneeling next to him, and above them he could see Neville and Professor Lupin watching. Harry felt very sick; when he put up his hand to push his glasses back on, he felt cold sweat on his face.
Ron and Hermione heaved him back onto his seat.
“Are you okay?” Ron asked nervously.
“Yeah,” said Harry, looking quickly toward the door. The hooded creature had vanished. “What happened? Where’s that—that thing? Who screamed?”
“No one screamed,” said Ron, more nervously still.
Harry looked around the bright compartment. Ginny and Neville looked back at him, both very pale.
“But I heard screaming—”
A loud snap made them all jump. Professor Lupin was breaking an enormous slab of chocolate into pieces.
“Here,” he said to Harry, handing him a particularly large piece. “Eat it. It’ll help.”
Harry took the chocolate but didn’t eat it.
“What was that thing?” he asked Lupin.
“A Dementor,” said Lupin, who was now giving chocolate to everyone else. “One of the Dementors of Azkaban.”