Harry Potter and the Methods of Rationality

Susan's voice rose again in incantation. There was a huge indignant bellow, and unknown voices began to yell.

Then Harry was through, his hand reaching into his pouch and his voice was saying "broomstick", as behind him the great doors began to swing shut again.

Harry continued running through the Entrance Hall even as the long three-person broomstick and its sets of stirrups began to protrude from the pouch, repeating a number of swearwords in his head and thinking this is what happens when you try to be sensible with the part of his mind that wasn't trying to figure out a search pattern to cover places where Hermione might be. The Library was on the third floor and practically on the other side of the castle... Harry had almost reached the great marble staircase by the time the broomstick was in his hand and "Up!" he was in the air and accelerating up toward the second floor -

"Gah!" Harry screamed, and barely managed to spin his broom in the air so that he didn't impale one of the human figures lurking at the top of the stairs. There was a ghastly moment of trying not to fall off the broom, perform the twists that would keep him in the stirrups, despite being really close to the ground and having almost no room to maneuver and then -

"Fred? George?"

"We can't figure out how to find her!" one of the Weasley twins blurted, hands twisting in distress. "We snuck out because we thought we could find Miss Granger - there has to be a quick way to find anyone inside the Hogwarts castle, we're both sure of it - but we can't figure out what it is!"

Harry stared at both of them, from where he was hanging upside down from the broomstick where his desperate maneuver had brought him, and entirely by reflex his mouth said, "Well, why were you so sure you could find her?"

"We don't know!" cried the other Weasley twin.

"Have you been able to find people inside Hogwarts before?"

"Yes! We -" and the Weasley twin who was speaking stopped abruptly, both redheads staring off into the distance with a blank expression.

There was a thundering crash, as of two huge doors being shoved open by someone very, very strong.

Harry spun around in the air to present the two open stirrup-positions on the broomstick to the Weasley twins, he didn't say anything, there was no reason for them to give away their positions if they didn't have to. Time seemed to move too slowly as the Weasley twins scrambled into the stirrups, Harry's heart beating hard despite his mental calculation that Mr. Hagrid, running, shouldn't reach even the foot of the stairway in time. Then the three of them were accelerating hard and away toward the nearest corridor, the stone floor beneath them blurring and the walls seeming to make an audible whooshing sound (though that was just the wind in their ears) as they went past; Harry remembered that he was riding a longer three-person broomstick barely in time to slow down for the next turn.

And now all the broomstick seats were occupied, but if they actually found Hermione then - Harry could put on the Cloak of Invisibility, that should hide him from the troll, and that would free up a seat for Hermione -

Harry ducked hard before a sudden archway took his head off.

"We found Jesse!" the Weasley twin seated behind Harry blurted. "I know we did! That time we needed to tell him that Filch was hunting for him!"

"How?" Harry said, most of his brain engaged in not dying in a horrible air accident. He should have slowed down for safety, but there was a tension rising in him, a sourceless dread. He couldn't slow down, something terrible would happen if he slowed down...

"We -" said the Weasley twin seated lower down. "We can't remember!"

Another sharp turn taken at, Harry estimated, roughly 0.3% of the speed of light, and they were going through a twisty curving corridor that Harry always took to get from the Great Hall to the library only it wasn't the shortest way if you were on a broomstick, he should've taken the long straight West Corridor instead -

The part of his brain that wasn't steering caught up with reality.

"Someone's been tampering with your minds!" Harry yelled, as he weaved through the curving corridor so fast that the tail-end Weasley sometimes lightly smacked into the wall as the length of the broomstick conflicted with Harry's maladapted air skills.

"What?" cried Fred or George.

"Whoever got to Hermione messed with your minds too!" It could be an Obliviation, it could be a False Memory that hadn't been planted right, but right now Harry couldn't think -

The broomstick turned and shot upward beside a spiral staircase, all three of them flattened themselves against the broomstick so they could make in through the gap in the ceiling that opened onto the third floor, and then they were in front of the library, the broomstick slowing to a halt with a shriek despite the lack of anything it could be friction-braking against. Harry shot the Weasley twins a quick glance to stay put, as he clambered off the broomstick to shove open the doors of the library, controlling his breathing as he shoved his head inside.

Hermione Granger wasn't there.

Madam Pince, who was eating a sandwich at her desk, looked up with a sudden glare. "Library's closed!"

"Have you seen Hermione Granger?" Harry said.

"I said the library's closed, boy! Lunch hours!"

"This is extremely important. Have you seen Hermione Granger or do you have any idea where she might be?"

"No, now be off!"

"Do you have any fast way of contacting Professor McGonagall in an emergency?"

"Eh?" said the librarian, startled. She rose up from behind her desk. "What is -"