The Promise Part 1 comic book takes place after Zuko is crowned Fire Lord, and Zuko makes Aang promise that if he ever start to turn into his father, Aang would kill him. Aang agrees, but he can't bring himself to do it. The Earth kingdom and Fire nation go to war, and Aang tries to stop them. Toph opens a metalbending academy with a few students, and teaches them how to metalbend with Sokka. I think that's mostly all that happens in the book.