Batgirl: A Matter of Family is a DLC story expansion from Batman: Arkham Knight. It was released via the Season Pass on July 14th, 2015 and was released for the general public on July 21st, 2015. The events of the story take place between Batman: Arkham Origins and Batman: Arkham Asylum.
Before her paralysis, Batgirl teams up with Robin to save her father, Commissioner James Gordon, from the clutches of the Joker, who has him kidnapped in an abandoned amusement park. Chronology-wise, this story is followed by the events of Batman: Assault on Arkham.