Eliezer Yudkowsky - Harry Potter and the Methods of Rationality

" Prismatis! " shouted Draco, raising his wand, and that shield you could see even through the water, a sparkling multicolored flat wall wide enough to shield Draco and the five other Dragons with him from the Chaotic force that had just started firing on them as they swam past, and that let the other five Dragons turn their attentions back to the Chaotic force they'd been chasing -

There was a tense moment as sleep spell after sleep spell crashed into Draco's Prismatic Wall, and Draco was hoping to Merlin that none of those four Chaotics had learned the Breaking Drill Hex -

Then there was the bell of a Dragon victory, and the Chaotic force spun head-for-foot and began swimming away; and Draco, his hands now shaking slightly, dropped the Prismatic Wall and lowered his wand.

Fighting in water was more exhausting even than fighting on broomsticks.

" Do not pursue! " Draco cried to his soldiers as they started to follow, then, " Sonorus! REFORM ON ME! "

The Dragon forces started converging on Draco, and the Chaotic forces spun around and began pursuing the Dragons on the instant - Draco swore out loud as he heard the bell of a Chaotic victory, someone hadn't gotten their Simple Shield oriented right - and then the Dragon forces were in supporting range of each other and the Chaotics were moving back into the murky distance.

Somehow, despite their numerical superiority, the Dragons had scored three times against the Chaotics and the Chaotics had scored four times back, and he'd heard one Dragon spy get executed. Either Harry Potter had thought of a lot of very good ideas very fast, or for some unimaginable reason he'd already spent a lot of time working out how to fight underwater. This wasn't working, and Draco needed to rethink things.

It looked like everyone was having trouble aiming while swimming, too, the battle might last long enough that time would be called... the distant underwater moon was only half full now, that wasn't good... he had to rethink things fast...

"What is it?" said Padma Patil, as she and her force swam over toward Draco.

Padma was his second-in-command; she was clever and powerful, and better yet, she hated Granger and saw Harry as a rival, which made her trustworthy. Working with Padma was making him realize the truth of the old adage that Ravenclaw was sister to Slytherin; Draco had been surprised when his father had told him it was an acceptable House for his future wife, but now he saw the sense of it.

"Wait until we're all here," Draco said. The truth was, he needed to catch his breath. That was the trouble with being the general and the most powerful wizard, you had to keep using magic.

Zabini came in next, commanding a force of two Sunnies and four Dragons, one of whom was Gregory keeping an eye on Zabini. Draco didn't trust Zabini. And neither Draco nor Zabini trusted the Sunnies enough to make them a majority of any unit; they were supposed to be loyal either to Draco directly, or to Granger who'd been fooled by the promise that the Dragons would be betrayed in the end after both forces had been depleted, just as Harry's more trusted Chaotics should've been fooled into not shooting at the Sunnies by the promise of their firing fake Sleep Hexes and switching to support Chaos later; but it was possible some of the Sunnies were loyal to Chaos and weren't firing real Sleep Hexes and that was why Dragon wasn't winning the way their numerical advantage should've let them win...

The next unit that approached was depleted, three soldiers holding wands on two other soldiers, who were swimming with empty hands.

Draco gritted his teeth. More traitor problems. He needed to talk to Professor Quirrell about having some way to punish traitors at least, conditions like these were unrealistic , in real life you tortured your traitors to death.

"General Malfoy!" shouted the commander of the problem unit as it swam up, a Ravenclaw boy named Terry. "We don't know what to do - Cesi shot Bogdan, but Cesi says Kellah told him that Bogdan shot Specter -"

"I didn't! " said Kellah.

"Yes you did! " shrieked Cesi. "General Malfoy, she's the spy, I should've rea-"

" Somnium, " said Draco.

There was the triple bell of a one-point loss from Dragon, and then Kellah's limp body began to float away in the water.

Draco had heard the word 'recursion' by this point, and he knew a Harry Potter plot when he saw one.

(Unfortunately Draco had not heard of autoimmune disorders, and the thought did not readily occur to him that a clever virus would begin its attack by creating symptoms of an autoimmune disorder so as to get the body to distrust its own immune system...)

" General order! " said Draco, raising his voice. "Nobody gets to shoot spies except myself, Gregory, Padma, and Terry. If anyone sees anything suspicious they come to one of us. "

And then -

There was the bell of Sunshine scoring two points.

" What? " said Draco and Zabini around the same time; their heads swiveled around. No one seemed to have gotten hit, and all the Sunshine soldiers were present and accounted for. (Except Parvati, who had been shot by some still-unknown traitor in Padma's squad; and of course Padma had shot Parvati again in case she was faking, so it wasn't her...)

"A Sunny traitor in Chaos?" said Zabini, sounding puzzled. "But all the ones I knew about were supposed to strike during Chaos's attack on Sunshine -"

"No!" said Padma in a tone of sudden realization. "That was Chaos executing a spy!"

" What? " said Zabini. "But why -"

And Draco got it. Damn it! "Because Potter thinks he's safe for how much he beats Sunshine, but not for how much he beats us! So he doesn't want to lose a single point when he executes a traitor! General order! If you have to execute a traitor, call Sunshine first! And don't forget to switch back to Dragon afterward -"

Granger: 253 / Malfoy: 252 / Potter: 252

Longbottom's body drifted chaotically through the water, arms and legs disarrayed. After Draco had finally got a hit in they'd all shot him again just to be sure.

Nearby was Harry Potter, now protected by a Prismatic Sphere, looking at them all grimly as the last sliver of crescent moon slowly diminished, somewhere far away. If Longbottom had managed to shoot one more soldier (Draco knew Harry was thinking), if the two Chaotics had managed to hold out just a little longer, they might have won ...

After Draco had reformed his forces and struck out again, the ensuing battle and execution of spies in Sunshine's name had left Sunshine exactly one point ahead of Dragon and Chaos both. Once Harry had started doing it, Draco had been left with no choice but to follow suit.

But now they had General Chaos outnumbered three to one, the survivors of Dragon Army and the last remaining Sunny traitor: Draco, and Padma, and Zabini.

And Draco, who was no fool, had ordered Padma to take Zabini's wand after Longbottom had shot Gregory and fallen in turn to Draco. The boy had given him an insulted look, told Draco that he owed him for this, and handed it over.

That left Draco and Padma to take down General Chaos.

"I don't suppose you'd like to surrender?" said Draco, smiling as evilly as any smile he'd ever directed at Harry Potter.

"Sleep before surrender!" shouted General Chaos.

"Just so you know," said Draco, "Zabini doesn't actually have an older sister for you to rescue from Gryffindor bullies. But Zabini does have a mother who doesn't approve of Muggleborns like Granger, and I wrote her a few notes, and offered Zabini a few favors - nothing involving my father, just things I can do in school. And by the way, Zabini's mother doesn't approve of the Boy-Who-Lived, either. Just in case you still thought Zabini was really on your side."