Avatar: The Last Airbender Episode Guide
[via wiki]
Sokka, Katara, and Yue follow Zuko to save Aang. In the Spirit World, Aang learns the identities of the Moon and Ocean spirits and that they are in danger. As Aang returns to the real world, he is saved by Katara. Meanwhile, Zhao succeeds in capturing the Moon Spirit, the source of all waterbending. Aang enters the Avatar State to destroy the siege, Zuko defeats Zhao, and Yue gives her life back to the Moon Spirit to save the Water Tribe.