Eliezer Yudkowsky - Harry Potter and the Methods of Rationality

A luminous moonlit cat leaped into existence and landed in front of Harry's Patronus. Harry almost screamed, which wouldn't have helped his image with Bellatrix.

"Harry!" said the voice of Professor McGonagall, sounding as alarmed as Harry had ever heard from her. "Where are you? Are you all right? This is my Patronus, answer me!"

With a convulsive effort, Harry cleared his mind, repurposed his throat, forced calm, swapped in a different personality like an Occlumency barrier. It took a few seconds and he hoped like hell that Professor McGonagall didn't notice a problem with that thanks to the communications delay, just as he hoped like hell that Patronuses didn't report on their surroundings.

A young boy's innocent voice said, "I'm in Mary's Place, Professor, in Diagon Alley. Going to the restroom actually. What's wrong?"

The cat leaped away, and Bellatrix began to chuckle softly, dusty appreciative laughter, but she cut herself off abruptly at a hiss from Harry.

A moment later the cat returned, and said in Professor McGonagall's voice, "I'm coming to pick you up right now. Don't go anywhere , if you're not around the Defense Professor don't go back to him, don't say anything to anyone, I'll be there as quickly as I can!"

And the bright cat blurred forward and vanished.

Harry glanced down at his watch, noting down the time, so that after he got everyone out of here, and Professor Quirrell anchored the Time-Turner again, he could go back and be in the restroom of Mary's Place at the appropriate time...

You know, said the problem-solving part of his brain, there's a limit to how many constraints you can add to a problem before it really is impossible, you know that?

It shouldn't have mattered, and it didn't really, it didn't compare to the suffering of a single prisoner in Azkaban, and yet Harry still found himself feeling very aware that if his plan didn't end with him being picked up from Mary's Place just like he'd never left, and the Defense Professor looking completely innocent of any and all wrongdoing, Professor McGonagall was going to kill him.

As their team prepared to eat another bite of territory out of C spiral, shielding and scanning before dispelling the previous shield to their rear, Amelia was tapping her fingers on her hip and wondering if she ought to consult the obvious expert. If only he wasn't so -

Amelia heard the familiar crack of fire and knew what she would see as she turned.

A third of her Aurors were spinning around and leveling their wands on the old wizard in half-moon glasses and a long silver beard who had appeared directly within their midst, a bright red-golden phoenix on his shoulder.

"Hold your fire!" Polyjuice made it easy to forge the face, but faking the phoenix travel would have been rather more difficult - the wards permitted it as one of the fast ways into Azkaban, though there were no fast ways out.

The old witch and the old wizard stared at each other for a long moment.

(Amelia wondered, in the back of her mind, which of her Aurors had sent the word, there were several former members of the Order of the Phoenix with her; she tried to remember, in the back of her mind, if she'd seen Emmeline's sparrow or Andy's cat missing from the flock of bright creatures; but she knew that it was futile. It might not even be any of her people, for the old meddler often knew things he had no way at all of knowing.)

Albus Dumbledore inclined his head to Amelia in a courteous gesture. "I hope I am not unwelcome here," the wizard said calmly. "We are all on the same side, are we not?"

"That depends," Amelia said in a hard voice. "Are you here to help us catch criminals, or to protect them from the consequences of their actions?" Are you going to try to stop the killer of my brother from getting her well-deserved Kiss, old meddler? From what Amelia heard, Dumbledore had gotten smarter toward the end of the war, mostly due to Mad-Eye's nonstop nagging; but had relapsed into his foolish mercies the instant Voldemort's body was found.

A dozen small points of white and silver, reflections of the shining animals, gleamed off the old wizard's half-moon glasses as he spoke. "Even less than you would I see Bellatrix Black freed," the old wizard said. "She must not leave this prison alive, Amelia."

Before Amelia could speak again, even to express her surprised gratification, the old wizard gestured with his long black wand and a blazing silver phoenix sprang into existence, brighter perhaps than all their other Patronuses put together. It was the first time she'd seen that spell cast wordlessly. "Order all your Aurors to cancel their Patronus Charms for ten seconds," said the old wizard. "What darkness cannot find, the light may."

Amelia snapped off the order to the communications officer, who would notify all Aurors through their mirrors, commanding Dumbledore's will to be done.

That took a few moments, and it became a period of awful silence, none of the Aurors daring to speak, while Amelia tried to weigh her own thoughts. She must not leave this prison alive... Albus Dumbledore wouldn't turn into Bartemius Crouch without a strong reason. If he'd meant to tell her why , he already would have; but it certainly wasn't a positive sign.

Still, it was good to know they'd be able to work together on this one.

"Now," said a chorus of mirrors, and all the Patronus Charms winked out except that blazing silver phoenix.

"Is there another Patronus still present?" the old wizard said clearly to the bright creature.

The bright creature dipped its head in a nod.

"Can you find it?"

The silver head nodded again.

"Will you remember it, should it depart and come again?"

A final nod from the blazing phoenix.

"It is done," Dumbledore said.

"Over," said all the mirrors a moment later, and Amelia raised her wand and began recasting her own Patronus. (Though it took some extra concentration, with that wolfish smile already on her face, to think of the first time Susan had kissed her cheek, instead of dwelling on the looming fate of Bellatrix Black. That other Kiss was a happy thought indeed, but not quite the right kind for the Patronus Charm.)

They hadn't even gotten to the end of that corridor before Harry's Patronus raised its hand, politely, as though in a classroom.

Harry thought quickly. The question was how to - no, that was also obvious.

"It seems," Harry said in a coldly amused voice, "that someone has instructed this Patronus to speak its message only to me." He chuckled. "Well then. Pardon me, dear Bella. Quietus. "

At once the silver humanoid said in Harry's own voice, "There is another Patronus which seeks this Patronus."

" What? " said Harry. And then, without pausing to think about what was happening, "Can you block it? Stop it from finding you?"

The silver humanoid shook its head.

No sooner did Amelia and the other Aurors finish recasting their Patronus Charms, when -

The blazing silver phoenix flew off, and the true red-golden phoenix followed it, and the old wizard calmly strode after both of them with his long wand gripped low.

The shields around their territory parted around the old wizard like water, and closed behind him with hardly a ripple.

" Albus! " shouted Amelia. "What do you think you're doing?"

But she already knew.

"Do not follow me," the old wizard's voice said sternly. "I can protect myself, I cannot protect others."

The curse Amelia shouted after him made even her own Aurors flinch.

This isn't fair, isn't fair, isn't fair! There's a limit to how many constraints you can add to a problem before it really is impossible!

Harry blocked off the useless thoughts, ignored the fatigue he was feeling, and forced his mind to confront the new requirements, he had to think fast, use the adrenaline on following the chains of logic quickly and without hesitation, instead of wasting it on despair.