Human Order of Guardians: Howling Shadows

After the events four years ago, Jackie didn't think she'd ever have to take up arms again. She was wrong. After a mysterious call from one of the Heads, Jackie starts a journey to the North Pole, alone, with HOG's fate in the balance. Who is this new immortal? Does he have Descendants? If so, are they a threat? Ideally read after the first arc, just so you know the characters.