Avatar: The Last Airbender - The Search Part 3 book by Gene Luen Yang

Avatar Aang travels to the spirit world to parley with an ancient power; bringing Fire Lord Zuko ever closer to discovering the truth about his mother's fate—and his own past. Yet Zuko's sister Azula is becoming increasingly dangerous; threatening to ruin everything that Zuko; Aang; Katara; and Sokka have struggled to achieve on their search! * The official continuation of Airbender from its creators; Michael Dante DiMartino and Bryan Konietzko! Published By Dark Horse Comics on 2013-11-12