Harry Potter and the Methods of Rationality

"In particular," Harry said, lowering his voice even further, "I'm not entirely sure that they wouldn't just report what I said to Lucius."

"Father wouldn't do that!" Draco said, looking genuinely aghast. "They're mine!"

"I'm sorry, Draco," Harry said. "I'm just not sure I can believe everything you believe about your father. Imagine it was your secret and me telling you my father wouldn't do that."

Draco nodded slowly. "You're right. I'm sorry, Harry. It was wrong of me to ask it of you."

How did I get this promoted? Shouldn't he hate me now? Harry had the feeling he was looking at something exploitable... he just wished his brain wasn't so exhausted. Ordinarily he would have loved to try his hand at some complicated plotting.

"Anyway," Harry said. "Trade. I tell you a fact that isn't on the grapevine, and does not go on the grapevine, and in particular does not go to your father, and in return you tell me what you and Slytherin think about the whole business."

"Deal!"

Now to make this as vague as possible... something that wouldn't hurt much even if it did get out... "What I said was true. I did discover one of Severus's secrets, and I did do some blackmail. But Severus wasn't the only person involved."

"I knew it!" Draco said exultantly.

Harry's stomach sank. He had apparently said something very significant and he did not know why. This was not a good sign.

"All right," Draco said. He was grinning widely now. "So here's what the reaction was like in Slytherin. First, all the idiots were like, 'We hate Harry Potter! Let's go beat him up!'"

Harry choked. "What is wrong with the Sorting Hat? That's not Slytherin, it's Gryffindor -"

"Not all children are prodigies," Draco said, though he was smiling in a sort of nasty-conspiratorial way, as though to suggest that he privately agreed with Harry's opinion. "And it took around fifteen seconds for someone to explain to them why this might not be such a favor to Snape, so you're fine. Anyway, after that was the second wave of idiots, the ones who were saying, 'Looks like Harry Potter was just another do-gooder after all.'"

"And then?" Harry said, smiling even though he had no idea why that was stupid.

"And then the actual smart people started talking. It's obvious that you found a way to put a lot of pressure on Snape. And while that could be more than one thing... the obvious next thought is that it has something to do with Snape's unknown hold over Dumbledore. Am I right?"

"No comment," Harry said. At least his brain was processing this part correctly. House Slytherin had wondered why Severus wasn't getting fired. And they'd concluded that Severus was blackmailing Dumbledore. Could that actually be true...? But Dumbledore hadn't seemed to act like it...

Draco went on talking. "And the next thing the smart people pointed out was that if you could put enough pressure on Snape to make him leave half of Hogwarts alone, that meant you probably had enough power to get rid of him entirely, if you wanted. What you did to him was a humiliation, just the same way he tried to humiliate you - but you left us our Head of House."

Harry made his smile wider.

"And then the really smart people," Draco said, his face now serious, "went off and had a little discussion by themselves, and someone pointed out that it would be a very stupid thing to leave an enemy around like that. If you could break his hold over Dumbledore, the obvious thing would be to just do it. Dumbledore would kick Snape out of Hogwarts and maybe even have him killed, he'd be very grateful to you, and you wouldn't have to worry about Snape sneaking into your dorm room at night with interesting potions."

Harry's face was now neutral. He had not thought of that and he really, really should have. "And from this you concluded...?"

"Snape's hold was some secret of Dumbledore's and you've got the secret!" Draco was looking exultant. "It can't be powerful enough to destroy Dumbledore entirely, or Snape would have used it by now. Snape refuses to use his hold for anything except staying king of Slytherin House in Hogwarts, and he doesn't always get what he wants even then, so it must have limits. But it's got to be really good! Father's been trying to get Snape to tell him for years!"

"And," Harry said, "now Lucius thinks maybe I can tell him. Did you already get an owl -"