Harry Potter and the Methods of Rationality

who?"

"Bless my soul," whispered the old barman. "Harry Potter... what an honour."

Harry blinked, then rallied. "Well, yes, you're quite perceptive; most people don't realise that so quickly -"

"That's enough," Professor McGonagall said. Her hand tightened on Harry's shoulder. "Don't pester the boy, Tom, he's new to all this."

"But it is him?" quavered an old woman. "It's Harry Potter?" With a scraping sound, she got up from her chair.

"Doris -" McGonagall said warningly. The glare she shot around the room should have been enough to intimidate anyone.

"I only want to shake his hand," the woman whispered. She bent low and stuck out a wrinkled hand, which Harry, feeling confused and more uncomfortable than he ever had in his life, carefully shook. Tears fell from the woman's eyes onto their clasped hands. "My granson was an Auror," she whispered to him. "Died in seventy-nine. Thank you, Harry Potter. Thank heavens for you."

"You're welcome," Harry said automatically, and then he turned his head and shot Professor McGonagall a frightened, pleading look.

Professor McGonagall slammed her foot down just as the general rush was about to start. It made a noise that gave Harry a new referent for the phrase "Crack of Doom", and everyone froze in place.

"We're in a hurry," Professor McGonagall said in a voice that sounded perfectly, utterly normal.

They left the bar without any trouble.

"Professor?" Harry said, once they were in the courtyard. He had meant to ask what was going on, but oddly found himself asking an entirely different question instead. "Who was that pale man, by the corner? The man with the twitching eye?"

"Hm?" said Professor McGonagall, sounding a bit surprised; perhaps she hadn't expected that question either. "That was Professor Quirinus Quirrell. He'll be teaching Defence Against the Dark Arts this year at Hogwarts."

"I had the strangest feeling that I knew him..." Harry rubbed his forehead. "And that I shouldn't ought to shake his hand." Like meeting someone who had been a friend, once, before something went drastically wrong... that wasn't really it at all, but Harry couldn't find words. "And what was... all of that?"

Professor McGonagall was giving him an odd glance. "Mr. Potter... do you know... how much have you been told... about how your parents died?"

Harry returned a steady look. "My parents are alive and well, and they always refused to talk about how my genetic parents died. From which I infer that it wasn't good."

"An admirable loyalty," said Professor McGonagall. Her voice went low. "Though it hurts a little to hear you say it like that. Lily and James were friends of mine."

Harry looked away, suddenly ashamed. "I'm sorry," he said in a small voice. "But I have a Mum and Dad. And I know that I'd just make myself unhappy by comparing that reality to... something perfect that I built up in my imagination."

"That is amazingly wise of you," Professor McGonagall said quietly. "But your genetic parents died very well indeed, protecting you."

Protecting me?

Something strange clutched at Harry's heart. "What... did happen?"

Professor McGonagall sighed. Her wand tapped Harry's forehead, and his vision blurred for a moment. "Something of a disguise," she said, "so that this doesn't happen again, not until you're ready." Then her wand licked out again, and tapped three times on a brick wall...

...which hollowed into a hole, and dilated and expanded and shivered into a huge archway, revealing a long row of shops with signs advertising cauldrons and dragon livers.

Harry didn't blink. It wasn't like anyone was turning into a cat.

And they walked forwards, together, into the wizarding world.

There were merchants hawking Bounce Boots ("Made with real Flubber!") and "Knives +3! Forks +2! Spoons with a +4 bonus!" There were goggles that would turn anything you looked at green, and a lineup of comfy armchairs with ejection seats for emergencies.

Harry's head kept rotating, rotating like it was trying to wind itself off his neck. It was like walking through the magical items section of an Advanced Dungeons and Dragons rulebook (he didn't play the game, but he did enjoy reading the rulebooks). Harry desperately didn't want to miss a single item for sale, in case it was one of the three you needed to complete the cycle of infinite wish spells.

Then Harry spotted something that made him, entirely without thinking, veer off from the Deputy Headmistress and start heading straight into the shop, a front of blue bricks with bronze-metal trim. He was brought back to reality only when Professor McGonagall stepped right in front of him.

"Mr. Potter?" she said.

Harry blinked, then realised what he'd just done. "I'm sorry! I forgot for a moment that I was with you instead of my family." Harry gestured at the shop window, which displayed fiery letters that shone piercingly bright and yet remote, spelling out Bigbam's Brilliant Books. "When you walk past a bookshop you haven't visited before, you have to go in and look around. That's the family rule."

"That is the most Ravenclaw thing I have ever heard."

"What?"

"Nothing. Mr. Potter, our first step is to visit Gringotts, the bank of the wizarding world. Your genetic family vault is there, with the inheritance your genetic parents left you, and you'll need money for school supplies." She sighed. "And, I suppose, a certain amount of