News of a traitor puts the trio at odds in Omashu, where a mechanist and rebels with a charming leader muddle their plans to protect the Earth Kingdom.

When the group lands in the Spirit World for a rescue mission, they come face to face with dangerous threats, painful memories and a mysterious entity.

As an attack on the Northern Water Tribe looms, Katara challenges a master Waterbender, Sokka meets a princess, and Aang takes Kuruk's words to heart.