"Glehhahhh..."
Professor McGonagall offered him a few more pleasantries, demanded a few more promises to which Harry nodded, said something about not talking to snakes where anyone could hear him, reminded him to read the pamphlet, and then somehow Harry found himself standing outside her office with the door closed firmly behind him.
"Gaahhhrrrraa..." Harry said.
Why yes his mind was blown.
Not least by the fact that, if not for the Prank, he might well have never obtained a Time-Turner in the first place.
Or would Professor McGonagall have given it to him anyway, only later in the day, whenever he got around to asking about his sleep disorder or telling her about the Sorting Hat's message? And would he, at that time, have wanted to pull a prank on himself which would have led to him getting the Time-Turner earlier? So that the only self-consistent possibility was the one in which the Prank started before he even woke up in the morning...?
Harry found himself considering, for the first time in his life, that the answer to his question might be literally inconceivable. That since his own brain contained neurons that only ran forwards in time, there was nothing his brain could do, no operation it could perform, which was conjugate to the operation of a Time Turner.
Up until this point Harry had lived by the admonition of E. T. Jaynes that if you were ignorant about a phenomenon, that was a fact about your own state of mind, not a fact about the phenomenon itself; that your uncertainty was a fact about you, not a fact about whatever you were uncertain about; that ignorance existed in the mind, not in reality; that a blank map did not correspond to a blank territory. There were mysterious questions, but a mysterious answer was a contradiction in terms. A phenomenon could be mysterious to some particular person, but there could be no phenomena mysterious of themselves. To worship a sacred mystery was just to worship your own ignorance.
So Harry had looked upon magic and refused to be intimidated. People had no sense of history, they learned about chemistry and biology and astronomy and thought that these matters had always been the proper meat of science, that they had never been mysterious. The stars had once been mysteries. Lord Kelvin had once called the nature of life and biology - the response of muscles to human will and the generation of trees from seeds - a mystery "infinitely beyond" the reach of science. (Not just a little beyond, mind you, but infinitely beyond. Lord Kelvin certainly had felt a huge emotional charge from not knowing something.) Every mystery ever solved had been a puzzle from the dawn of the human species right up until someone solved it.
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.
No doubt you are already thinking of all manner of wonderful pranks, as your father committed in his day. If his full misdeeds were known, every woman in Gryffindor would gather to desecrate his grave. I shall not try to stop history from repeating, but be MOST careful not to reveal yourself. If Dumbledore saw a chance to possess one of the Deathly Hallows, he would never let it escape his grasp until the day he died.
A Very Merry Christmas to you.
The note was unsigned.
"Hold on," Harry said, pulling up short as the other boys were about to leave the Ravenclaw dorm. "Sorry, there's something else I've got to do with my trunk. I'll be along to breakfast in a couple of minutes."
Terry Boot scowled at Harry. "You'd better not be planning to go through any of our things."
Harry held up one hand. "I swear that I intend to do nothing of the sort to any of your things, that I only intend to access objects that I myself own, that I have no pranking or otherwise questionable intentions towards any of you, and that I do not anticipate those intentions changing before I get to breakfast in the Great Hall."