This episode is part of the Avatar Book Three - Fire
Avatar The Last Airbender Episode Guide ~ via Wiki
Zuko and Katara confront Azula, but she challenges Zuko to a one-on-one Agni Kai. Zuko is wounded by a blast of lightning while protecting Katara. Meanwhile, Aang finally confronts Ozai but finds himself overwhelmed by Ozai’s comet-enhanced Firebending. Sokka, Toph, and Suki attempt to halt the fleet but are soon separated, while the Order of the White Lotus battles for Ba Sing Se.