Harry Potter and the Methods of Rationality

'You don't mean...' gasped Harry. 'My father... owned another rock?'

'Excuse me,' said Dumbledore, 'I am still older and more mysterious than you and if there are any revelations to be made then I will do the revealing, thank you... oh, where is that thing!' Dumbledore reached down further into the desk drawer, and still further. His head and shoulders and whole torso disappeared inside until only his hips and legs were sticking out, as though the desk drawer was eating him.

Harry couldn't help but wonder just how much stuff was in there and what the complete inventory would look like.

Finally Dumbledore rose back up out of the drawer, holding the objective of his search, which he set down on the desk alongside the rock.

It was a used, ragged-edged, worn-spined textbook: Intermediate Potion Making by Libatius Borage. There was a picture of a smoking vial on the cover.

'This,' Dumbledore intoned, 'was your mother's fifth-year Potions textbook.'

'Which I am to carry with me at all times,' said Harry.

'Which holds a terrible secret. A secret whose revelation could prove so disastrous that I must ask you to swear - and I do require you to swear it seriously, Harry, whatever you may think of all this - never to tell anyone or anything else.'

Harry considered his mother's fifth-year Potions textbook, which, apparently, held a terrible secret.

The problem was that Harry did take that oaths like that very seriously. Any vow was an Unbreakable Vow if made by the right sort of person.

And...

'I'm feeling thirsty,' Harry said, 'and that is not at all a good sign.'

Dumbledore entirely failed to ask any questions about this cryptic statement. 'Do you swear, Harry?' said Dumbledore. His eyes gazed intently into Harry's. 'Otherwise I cannot tell you.'

'Yes,' said Harry. 'I swear.' That was the trouble with being a Ravenclaw. You couldn't refuse an offer like that or your curiosity would eat you alive, and everyone else knew it.

'And I swear in turn,' said Dumbledore, 'that what I am about to tell you is the truth.'

Dumbledore opened the book, seemingly at random, and Harry leaned in to see.

'Do you see these notes,' Dumbledore said in a voice so low it was almost a whisper, 'written in the margins of the book?'

Harry squinted slightly. The yellowing pages seemed to be describing something called a potion of eagle's splendour, many of the ingredients being items that Harry didn't recognise at all and whose names didn't appear to derive from English. Scrawled in the margin was a handwritten annotation saying, I wonder what would happen if you used Thestral blood here instead of blueberries? and immediately beneath was a reply in different handwriting, You'd get sick for weeks and maybe die.

'I see them,' said Harry. 'What about them?'

Dumbledore pointed to the second scrawl. 'The ones in this handwriting,' he said, still in that low voice, 'were written by your mother. And the ones in this handwriting,' moving his finger to indicate the first scrawl, 'were written by me. I would turn myself invisible and sneak into her dorm room while she was sleeping. Lily thought one of her friends was writing them and they had the most amazing fights.'

That was the exact point at which Harry realised that the Headmaster of Hogwarts was, in fact, crazy.

Dumbledore was looking at him with a serious expression. 'Do you understand the implications of what I have just told you, Harry?'

'Ehhh...' Harry said. His voice seemed to be stuck. 'Sorry... I... not really...'

'Ah well,' said Dumbledore, and sighed. 'I suppose your cleverness has limits after all, then. Shall we all just pretend I didn't say anything?'

Harry rose from his chair, wearing a fixed smile. 'Of course,' Harry said. 'You know it's actually getting rather late in the day and I'm a bit hungry, so I should be going down to dinner, really' and Harry made a beeline for the door.

The doorknob entirely failed to turn.

'You wound me, Harry,' said Dumbledore's voice in quiet tones that were coming from right behind him. 'Do you not at least realise that what I have told you is a sign of trust?'

Harry slowly turned around.

In front of him was a very powerful and very insane wizard with a long silver beard, a hat like a squashed giant mushroom, and wearing what looked to Muggle eyes like three layers of bright pink pyjamas.

Behind him was a door that didn't seem to be working at the moment.

Dumbledore was looking rather saddened and weary, like he wanted to lean on a wizard's staff he didn't have. 'Really,' said Dumbledore, 'you try anything new instead of following the same pattern every time for a hundred and ten years, and people all start running away.' The old wizard shook his head in sorrow. 'I'd hoped for better from you, Harry Potter. I'd heard that your own friends also think you mad. I know they are mistaken. Will you not believe the same of me?'

'Please open the door,' Harry said, his voice trembling. 'If you ever want me to trust you again, open the door.'

There was the sound behind him of a door opening.