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. Amelia was sitting on the floor near one of the chairs, trembling slightly muttering rude words under her breath. 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.

"What?" asked Amelia, just as confused as Harry. 

Harry looked around the bright compartment. Ginny and Neville looked back at him, both very pale.

"But I heard screaming --"

"I heard it," Amelia and Harry glanced at each other. 

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."

Amelia muttered a vulgar word under her breath.

Everyone stared at him. Professor Lupin crumpled up the empty chocolate wrapper and put it in his pocket.

"Eat," he repeated. "It'll help. I need to speak to the driver, excuse me...