An Airbender comes to grips with his new reality as war erupts. A century later, a pair of Water Tribe siblings make a discovery that changes everything.
Aang, Katara and Sokka arrive at a small island, home to elite warriors named after Avatar Kyoshi. The Fire Nation gets wind of the Avatar's whereabouts.
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.
In captivity, Aang meets a king with a taste for games. To find their friend, the siblings must navigate a dark tunnel - and put their differences aside.
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.