Eliezer Yudkowsky - Harry Potter and the Methods of Rationality

Harry took a deep breath, feeling the water gurgle harmlessly in his lungs.

They'd fought in the forest, and he hadn't gotten a chance to say it.

They'd fought in the corridors of Hogwarts, and he hadn't gotten a chance to say it.

They'd fought in the air, broomsticks issued to every soldier, and it still hadn't made sense to say it.

Harry had thought he wouldn't ever get to say those words, not while he was still young enough for them to be real...

The Chaos Legionnaires were looking at Harry in puzzlement, as their general swam with his feet pointing up toward the distant light of the surface, and his head pointed down toward the murky depths.

" Why are you upside down? " the young commander shouted at his army, and began to explain how to fight after you abandoned the privileged orientation of gravity.

A hollow, booming bell echoed through the water, and on the instant, Zabini and Anthony and five other soldiers struck out downward, into the murky depths of the lake. Parvati Patil, the only Gryffindor in the group, turned her head back for a moment and gave them all a cheery wave as she dived; and after a moment, Scott and Matt did the same. The rest just sank and vanished.

General Granger swallowed a lump in her throat as she watched them go. She was risking everything on this, dividing her army instead of just trying to take as many enemy soldiers with them as possible.

The thing to realize, Zabini had told her, was that no army would move until they had a plan that let them expect victory. Sunshine couldn't just plan to win themselves, they had to make both other armies think they would win until it was too late.

Ernie and Ron still looked like they were in shock. Susan was gazing after the disappearing soldiers with a calculating look. Her army, what was left of it, just looked bewildered, traceries of light dappling on their uniforms as they all drifted just below the sunlit surface of the lake.

" Now what?" said Ron.

"Now we wait," said Hermione, loudly enough for all the soldiers to hear. It felt odd to talk with her mouth full of water, she kept feeling like she was committing some sort of horrible impoliteness at the dinner table and was about to drool all over herself. "All of us left here are going to get zapped, but that was going to happen anyway with Dragon and Chaos ganging up on us. We've just got to take as many of them with us as we can."

"I've got a plan," said one of her Sunshine Soldiers... Hannah, her voice had been a little hard to recognize at first. "It's like all complicated, but I know how we can get Dragon and Chaos to start fighting each other -"

"Me too!" said Fay. "I've got a plan too! See, Neville Longbottom is secretly on our side -"

" You were talking to Neville?" said Ernie. "That's not right, I was the one who -"

Daphne Greengrass and a couple of other Slytherins who hadn't gone with Zabini were giggling helplessly as the cries of "No, wait, I was the one who got Longbottom" erupted from one soldier after another.

Hermione just looked at them all wearily.

"Okay," said Hermione when it had all died down, "does everyone get it? All your plots were faked by the Chaos Legion, or maybe some by Dragon. Anyone who really wanted to betray Harry or Malfoy went straight to me or Zabini, not you. Just go ahead and compare notes on all your secret plots and you'll see it for yourselves." She might not be as good at plotting as Zabini, but she could always understand what all her officers told her, that was why Professor Quirrell had made her the general. "So don't bother trying to do any plots when the other armies get here. Just fight, okay? Please?"

"But," said Ernie with shock on his face, "Neville is in Hufflepuff! You're saying he lied to us?"

Daphne was laughing so hard and so helplessly that the exhalations had turned her upside down in the water.

"I'm not sure what Longbottom is," said Ron darkly, "but I don't think he's a Hufflepuff any more. Not now that Harry Potter's got to him."

"Do you know," said Susan, "I asked him that, and Neville told me he had become a Chaos Hufflepuff?"

" Anyway ," said Hermione in a loud voice. "Zabini took with everyone who we thought was a spy, so in our army we can stop watching each other quite so hard now, I hope."

" Anthony was a spy?" yelled Ron.

" Parvati was a spy?" gasped Hannah.

"Parvati was totally a spy," said Daphne. "She shopped at the spy shoe store and wore spy lipstick, and someday she's going to marry a nice spy husband and have a lot of little spies."

And then a gong sound echoed through the water, indicating that Sunshine had just scored two points.

This was shortly followed by the triple gong of Dragon losing a single point.

Traitors weren't allowed to kill generals, not after the disaster of the first battle in December when all three generals had been shot in the first minute. But with any luck...

"Aw," said Hermione. "It sounds like Mr. Crabbe is taking a little nap."

Like two shoals of fish, the armies swam along.

Neville Longbottom kicked his feet in slow, measured motions. Diving, always diving in whatever direction you happened to be moving. You wanted to show the enemy the smallest profile, present them with your head or your feet. So you were always diving, downward and head-first, and the enemy was always down.

Like every Chaos Legionnaire in the army, Neville's head was constantly rotating as he swam, looking up, down, around, to every side. Not just watching for Sunshine Soldiers, but watching for any sign that a Chaos Legionnaire had drawn their wand and was about to betray them. Usually traitors waited until the confusion of battle to make their move, but that early gong had put them all on guard.

...the truth was, Neville was feeling sad about that. In November he'd been a soldier in a united army, all of them pulling together and helping each other, and now they were all watching each other constantly for the first signs of betrayal. It might have been more fun for General Chaos, but it wasn't nearly as much fun for Neville.

The direction formerly known as 'up' was getting steadily brighter, as they came closer to the surface and Sunshine.

"Wands out," said General Chaos.

Neville's squad drew their wands, pointing them straight ahead toward the enemy, as their heads scanned around more rapidly. If there were Sunny traitors, the time was approaching for them to strike.

The other shoal of fish, Dragon Army, was doing the same thing.

" Now! " shouted the distant voice of the Dragon General.

" Now! " shouted General Chaos.

" For Sunshine!" shouted all the soldiers in both armies, and charged downward.

" What? " said Minerva involuntarily as she watched the screens from next to the lake, a cry echoed in many other places; all of Hogwarts was watching this battle as they had watched the first.

Professor Quirrell was laughing dryly. "I warned you, Headmaster. It is impossible to have rules without Mr. Potter exploiting them."

For long precious seconds, as the forty-seven soldiers charged her own seventeen, Hermione's mind went blank.

Why...

Then it all snapped into place.

Every time a soldier originally from Sunshine got shot by someone crying the name of Sunshine, she would lose a Quirrell point. When two Sunshine Soldiers were shot by either army, both enemy armies would be two points closer to overtaking her, it was the same gain only shared . And if anyone shot another soldier not in the name of Sunshine, that gong wouldn't get lost in the confusion...