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.

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.