J.K.

There was an uproar. It took several purple firecrackers exploding from the end of Professor Dumbledore’s wand to bring silence.
“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.”
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, all right,” he snapped. “But Percy’d better not see us.”
D

set off home

Mr Dursley might have been drifting into an uneasy sleep, but the cat on the wall outside was showing no sign of sleepiness. It was sitting as still as a statue, its eyes fixed unblinkingly on the far corner of Privet Drive. It didn’t so much as quiver when a car door slammed in the next street, nor when two owls swooped overhead.