Harry Potter and the Methods of Rationality

I, Draco, of Most Ancient House, demand redress, for that I have thrice over helped you and offered you only my goodwill, and in return you falsely accused me of plotting against you,

Draco had to stop and take a breath, forcing down the seething anger; he was starting to genuinely feel the insult now, and he'd just written out the last phrase and underlined it without thinking, like it was an ordinary letter. After a moment's reflection, he decided to let it stand; it might not be the exact formal phrasing but it had a raw, angry tone that seemed appropriate.

which insult you committed before the eyes of Britain.

Thus I, Draco, compel you, Hermione, by custom, by law, by

"The seventeenth ruling of the thirty-first Wizengamot," Draco said aloud without looking, a line delivered in many plays; he sat straighter as he said it, feeling every pulse of the noble blood in his veins.

Thus I, Draco, compel you, Hermione, by custom, by law, by the 17th ruling of the 31st Wizengamot, to meet me in wizard's duel with terms: That we each come alone and in silence, speaking to none before or after,

If the duel went poorly, Draco could just say nothing and leave it at that. And if he did defeat Granger, he would have learned experimentally that he could beat her again in a public challenge. It wasn't cheating, but it was Science, which was almost as good.

contesting by magic solely, without death or lasting injury,

...where? Draco had been told about a room in Hogwarts that was good for duels, where everything valuable was already protected by wards, and there were no portraits to tattle on you... which one had it been again...

in the trophy room of the Castle of the Hogwarts School of Witchcraft and Wizardry,

And their second and public duel had better be soon, like tomorrow, it would take very little time for his reputation in Slytherin to go irretrievably to sludge. He needed to fight Granger for the first time tonight.

upon midnight's stroke that shall end this very day.

Draco, of the Noble and Most Ancient House of Malfoy.

Draco signed the formal parchment, and then drew forth his ordinary and lesser parchment, and his regular ink, for his post scriptum:

If you don't know how the rules work, Granger, here's how it is. You insulted a Most Ancient House, and I've got the lawful right to challenge. And if you affront the conditions of the duel, like by having Flitwick show up at the trophy room, or even just telling anyone else, my father will take you and your false honor straight to the Wizengamot.

Draco Malfo

On the last letter his quill pressed down on the parchment so viciously that the nib snapped off, creating a streak of ink and a small rip in the parchment, which Draco decided also looked appropriate.

That night at dinnertime, Susan Bones came to Harry Potter and told him that she thought Draco Malfoy was going to carry out his plot against Hermione very soon. She was warning all the members of S.P.H.E.W., and she'd warned Professor Sprout, and she'd warned Professor Flitwick, and she was going to send a letter to her Aunt tonight, and now she was warning Harry Potter, too. Only they couldn't quite talk about it with Padma - Susan said, looking very serious - because Padma was feeling torn between her loyalty to Hermione and her loyalty to her General.

Harry James Potter-Evans-Verres, who was at this point feeling more frustrated with the entire situation than anything really productive, snapped at her that yes, he knew something had to be done.

After Susan Bones left, Harry looked over at the other end of the Ravenclaw table, where Hermione had sat down away from him or Padma or Anthony or any of her other friends.

But Hermione didn't look like she was in a mood where somebody going over and bothering her would be taken very well.