Professor Dumbledore sent all the Gryffindors back to the Great Hall, where they were joined ten minutes later by the students from Hufflepuff, Ravenclaw, and Slytherin, who all looked extremely confused.

"The teachers and I need to conduct a thorough search of the castle," Professor Dumbledore told them as Professors McGonagall and Flitwick closed all doors into the hall.

"I'm afraid that, for your own safety, you will have to spend the night here. I want the prefects to stand guard over the entrances to the hall and I am leaving the Head Boy and Girl in charge. Any disturbance should be reported to me immediately," he added Percy, who was looking immensely determined. "Send word with one of the ghosts."

Professor Dumbledore paused, about to leave the hall, and said, "Oh, yes, you'll be needing..."

One casual wave of his wand and the long tables flew to the edges of the hall and stood themselves against the walls; another wave, and the floor was covered with hundreds of squashy purple sleeping bags.

"Sleep well," said Professor Dumbledore, closing the door behind him.

The hall immediately began to buzz excitedly; the Gryffindors were telling the rest of the school what had just happened.

"Everyone into their sleeping bags!" shouted Percy. "Come on, now, no more talking! Lights out in ten minutes!"

"C'mon," Ron said to Arth, Harry, and Hermione; they seized three sleeping bags and dragged them into a corner.

"Do you think Black's still in the castle?" Hermione whispered anxiously.

"Dumbledore obviously thinks he might be," said Ron.

"It would be suicidal to hide in the school after attacking the fat lady... however, he could hide here for the very same reason. Because no one would expect it," arth muttered. "At least Dumbledore isn't taking any chances."

"It's very lucky he picked tonight, you know," said Hermione as they climbed fully dressed into their sleeping bags and propped themselves on their elbows to talk. "The one night we weren't in the tower..."

"I reckon he's lost track of time, being on the run," said Ron. "Didn't realize it was Halloween. Otherwise he'd have come bursting in here."

Arth scoffed at his words.

"That is so stupid to even consider. You think that a person who has the capability to break into one of the most heavily guarded places in the world will forget to check the date before invading a school?"

"Errr... he was too busy running away?"

Arth sighed.

"The ministry is no where near finding Black. He has been sighted a couple times but that does nothing to tell us where he is and how to catch him. They are literally walking around in circles for Sirius Black."

"So why would he attack today?"

"I don't know, but I refuse to believe that someone who could escape from Azkaban and as someone who went to Hogwarts would forget today was the Halloween feast."

Hermione raised an eyebrow.

"But then that means that what Black is looking for isn't a person-"

"But a thing," Arth finished. "That's exactly right. He isn't after Harry but for something that is in the school."

"But what?"

"I don't know? I'm not Sirius."

Arth stopped talking before straining his ears to listen to his surroundings.

Everyone else were asking one another the same question as them: "How did he get in?"

"Maybe he knows how to Apparate," said a Hufflepuff a few feet away. "Just appear out of thin air, you know."

"You idiot, you cant apparate in school grounds," Replied a Ravenclaw to his left.

"Disguised himself, probably," said an older Ravenclaw.

"He could've flown in," suggested Dean Thomas.

"Honestly, am I the only person who's ever bothered to read Hogwarts, A History?" said Hermione crossly to Harry and Ron.

"Just you and Arth probably," said Ron. "Why?"

"Because the castle's protected by more than walls, you know," said Hermione. "There are all sorts of enchantments on it, to stop people entering by stealth."

"You can't just Apparate in here. And I'd like to see the disguise that could fool those dementors. They're guarding every single entrance to the grounds," said Arth.

"They'd have seen him fly in too. And Filch knows all the secret passages, they'll have them covered..."

Arth frowned.

"Unless there is a secret passage that no one knows about except Black-"

"The lights are going out now!" Percy shouted. "I want everyone in their sleeping bags and no more talking!"

The candles all went out at once. The only light now came from the silvery ghosts, who were drifting about talking seriously to the prefects, and the enchanted ceiling, which, like the sky outside, was scattered with stars.

What with that, and the whispering that still filled the hall, Arth felt as though he were sleeping outdoors in a light wind. In fact, he felt as though he could hear the faint noise of someone gently tapping on a window. Arth opened his eyes and turned around to face the window.

Standing at the window was a familiar hooded figure staring into the great hall.

Arthur sighed.

"Hey Hermione, cover me."

"What?" Whispered Hermione furiously however, Arth was already gone.