While training in the North Pole, Aang and Katara hear reports of a waterbender, Hiryu, going missing, which they investigate. They arrive at the Water Tribe as a Fire Nation ship attacks, led by Prince Zuko. They are able to fend off the attackers, but Katara is captured during the battle. Aang and Sokka follow the ship, but are slowed by a Firebending machine.