The Shadow of Kyoshi (Avatar: the Last Airbender: the Kyoshi Novels, Band 2)

The epic, can't-miss follow-up to the New York Times bestselling Avatar: The Last Airbender: The Rise of Kyoshi
Kyoshi's place as the true Avatar has finally been cemented--but at a heavy cost. With her mentors gone, Kyoshi voyages across the Four Nations, struggling to keep the peace. But while her reputation grows, a mysterious threat emerges from the Spirit World. To stop it, Kyoshi, Rangi, and their reluctant allies must join forces before the Four Nations are destroyed irreparably.
This thrilling follow-up continues Kyoshi's journey from a girl of humble origins to the merciless pursuer of justice still feared and admired centuries after becoming the Avatar.