This is volume 4 of the Avatar Last Airbender series.
For years, fans of Avatar: The Last Airbender and The Legend of Korra have burned with one question-what happened to Fire Lord Zuko's mother? Finding a clue at last, Zuko enlists the aid of Team Avatar-and the most unlikely ally of all-to help uncover the biggest secret of his life.
80 page softcover DARK HORSE COMICS
(W) Gene Luen Yang & Various (A/CA) Gurihiru