Avatar - The Last Airbender - The Legacy of Yangchen - Chronicles of the Avatar - Book 4

Avatar Yangchen has succeeded in bringing a measure of stability to Bin-Er, but her successes have been limited to a single city, and rumors concerning Unanimity-a weapon capable of total obliteration-have led to increasing tensions among the Four Nations.
 
Desperate to restore diplomacy, Yangchen attempts to de-escalate hostilities between heads of state. But in the wake of a brutal assassination and the freeing of Unanimity, Yangchen is forced to bring Kavik-the trusted former companion whose betrayal crushed her-back into her fold.
 
As the Four Nations teeter on the brink of conflict and she begins to unravel the power-hungry Zongdu Chaisee's true agenda, Yangchen is forced to measure the worth of humanity and how much can be sacrificed in the name of balance.