Harry Potter and the Methods of Rationality

Now, for the first time, he was up against the prospect of a mystery that was threatening to be permanent. If Time didn't work by acyclic causal networks then Harry didn't understand what was meant by cause and effect; and if Harry didn't understand causes and effects then he didn't understand what sort of stuff reality might be made of instead; and it was entirely possible that his human mind never could understand, because his brain was made of old-fashioned linear-time neurons, and this had turned out to be an impoverished subset of reality.

On the plus side, the Comed-Tea, which had once seemed all-powerful and all-unbelievable, had turned out to have a much simpler explanation. Which he'd missed merely because the truth was completely outside his hypothesis space or anything that his brain had evolved to comprehend. But now he actually had figured it, probably. Which was sort of encouraging. Sort of.

Harry glanced down at his watch. It was nearly 11AM, he'd gotten to sleep last night at 1AM, so in the natural state of affairs he'd go to sleep tonight at 3AM. So to go to sleep at 10PM and wake up at 7AM, he should go back five hours total. Which meant that if he wanted to get back to his dorm at around 6AM, before anyone was awake, he'd better hurry up and...

Even in retrospect Harry didn't understand how he'd pulled off half the stuff involved in the Prank. Where had the pie come from?

Harry was starting to seriously fear time travel.

On the other hand, he had to admit that it had been an irreplaceable opportunity. A prank you could only pull on yourself once in a lifetime, within six hours of when you first found out about Time-Turners.

In fact that was even more puzzling, when Harry thought about it. Time had presented him with the finished Prank as a fait accompli, and yet it was, quite clearly, his own handiwork. Concept and execution and writing style. Every last part, even the ones he still didn't understand.

Well, time was a-wasting and there were at most thirty hours in a day. Harry did know some of what he had to do, and he might figure out the rest, like the pie, while he was working. There was no point putting it off. He couldn't exactly accomplish anything stuck here in the future.

Five hours earlier, Harry was sneaking into his dorm with his robes pulled up over his head as a thin sort of disguise, just in case someone was already up and about and saw him at the same time as Harry lying in his bed. He didn't want to have to explain to anyone about his little medical problem with Spontaneous Duplication.

Fortunately it seemed that everyone was still asleep.

And there also seemed to be a box, wrapped in red and green paper with a bright golden ribbon, lying next to his bed. The perfect, stereotypical image of a Christmas present, although it wasn't Christmas.

Harry crept in as softly as he could manage, just in case someone had their Quieter turned down low.

There was an envelope attached to the box, closed by plain clear wax without a seal impressed.

Harry carefully pried the envelope open, and took out the letter inside.

The letter said:

This is the Cloak of Invisibility of Ignotus Peverell, passed down through his descendants the Potters. Unlike lesser cloaks and spells it has the power to keep you hidden, not merely invisible. Your father lent it to me to study shortly before he died, and I confess that I have received much good use of it over the years.

In the future I shall have to get along with Disillusionment, I fear. It is time the Cloak was returned to you, its heir. I had thought to make this a Christmas present, but it wished to come back to your hand before then. It seems to expect you to have need of it. Use it well.