Harry Potter and the Methods of Rationality

"No," the old wizard said (even as she blurted "What?" and Severus lifted an eyebrow). "It would not have been enough, and now it is no debt at all. You are an Occlumens and cannot testify under Veritaserum. Draco Malfoy could be Obliviated of his own memory before he could testify -" Albus hesitated. "Harry... whatever you have done with Draco, you must assume that Lucius Malfoy will soon know of it."

Harry's head sank into his hands. "He'll give Draco Veritaserum."

"Yes," Albus said quietly.

The Boy-Who-Lived didn't say anything, as he sat with his head in his hands.

The Potions Master looked genuinely shocked. "Draco really was trying to help Miss Granger," Severus said. "You - Potter, you actually -"

"Turned him?" Harry said from between his hands. "I was about three-quarters done. Taught him the Patronus Charm and everything. I don't know what will happen now, though."

"Voldemort has struck a grave blow against us, this day," Albus said. The sound of old wizard's voice was like the look of the boy with his head in his hands. "He has taken two of our pieces, with one... No. I should have seen it earlier. He has taken two of Harry's pieces with one move. Voldemort has begun his game again, not against myself, but against Harry. Voldemort knows the prophecy, he knows who his last foe shall be. He is not waiting to face Hermione Granger and Draco Malfoy at Harry's side when they are grown. He is striking at them now."

"Maybe it's You-Know-Who and maybe it isn't," Harry said, his voice sounding a little unsteady. "Let's not narrow down the hypothesis space prematurely." Harry took a breath and lowered his hands. "The other thing we can try is to nail the real culprit before the trial - or at least find solid evidence that someone else did it."

"Mr. Potter," said Minerva, "Professor Quirrell told the Aurors that he knew of someone with a motive to harm Mr. Malfoy. Do you know who he was talking about?"

"Yes," Harry said, after a hesitation. "But I think I shall conduct that part of my investigation with the Defense Professor - just as I would not have Professor Quirrell in the room while we were discussing how to investigate him."

"He suspects me?" Severus said, then gave a short laugh. "Why, of course he does."

"My own plan," said Harry, "is to go look at the trophy room where the supposed duel took place and see if I can discover anything anomalous. If you can tell the investigating Aurors to let me through -"

"What investigating Aurors?" Severus said tonelessly.

Harry Potter took a deep breath, slowly let it out, and then spoke again. "In mystery books it usually takes longer than one day to solve a crime, but twenty-four hours is - no, thirty hours is eighteen hundred minutes. And I can think of at least one other important place to look for clues - though it'll have to be someone who can get into the Ravenclaw girls' dorm. Back when Hermione was fighting bullies, she was finding notes under her pillow each morning, telling her where to go -"

"Albus..." ground out Minerva.

"I did not send them," said the old wizard. His white eyebrows had lifted in surprise. "I knew nothing of this. You think she was being played, Harry?"

"It's a possibility," Harry said. "More so, because there's a part of this puzzle that you don't know about yet." Harry's voice lowered, grew more intense. "Headmaster, you already know that I got my father's invisibility cloak from someone who left a note under my pillow, saying it was an early Christmas present. I think we have to assume that's the same person who left notes for Hermione -"

"Harry," the old wizard said, and hesitated momentarily. "Returning your father's cloak to you, does not seem to me like the act of a villain -"

"Listen," Harry Potter said urgently. "The part you don't know is that after Bellatrix Black escaped from Azkaban, I found another note under my pillow, signed 'Santa Claus', saying that they'd heard you were shutting me up inside Hogwarts, and that they were giving me an escape route to the Salem Witches' Institute in America. That note came with a deck of cards, in which the King of Hearts was supposedly a portkey -"

"Mr. Potter!" cried Professor McGonagall, she hadn't even thought before she spoke. "That could well be a kidnapping attempt! You should have told - "