"Prefects," he rumbled, "lead your Houses back to the dormitories immediately!"

Percy was in his element.

"Follow me! Stick together, first years! No need to fear the troll if
you follow my orders! Stay close behind me, now. Make way, first years coming through! Excuse me, I'm a prefect!"

"How could a troll get in?" Harry asked as they climbed the stairs.

"Don't ask me, they're supposed to be really stupid," said Ron. "Maybe Peeves let it in for a Halloween joke."

"Maybe," Harry and Ron jumped at the sudden voice behind them," He has been dropping golf balls on me and putting snakes in my bed trying to annoy me hasn't worked though that loser," it was Amelia she had been at the Ravenclaw table. How she got over to them so fast Harry didn't know. 

They passed different groups of people hurrying in different directions. As they jostled their way through a crowd of confused Hufflepuffs, Harry suddenly grabbed Ron's arm.

"I've just thought -- Hermione." 

"What about her?"

"She doesn't know about the troll." Ron bit his lip.

"Oh shit!"

"Oh, all right," he snapped. "But Percy'd better not see us."

Ducking down, they joined the Hufflepuffs going the other way, slipped down a deserted side corridor, and hurried off toward the girls' bathroom. They had just turned the corner when they heard quick footsteps behind them.

"Percy!" hissed Ron, pulling Harry behind a large stone griffin who dragged Amelia with him.

Peering around it, however, they saw not Percy but Snape. He crossed the corridor and disappeared from view.

"What's he doing?" Harry whispered. "Why isn't he down in the dungeons with the rest of the teachers?"

"Search me."