Batgirl Annual (Rebirth) (2017-) #1

Batgirl and Supergirl must team up to break into Arkham Asylum! In this all-new Rebirth annual Batgirl must seek Supergirl’s help to solve a mystery that leads them to the heart of the most insane insane asylum there is! But what they discover—and who they discover—in Arkham will lead to a much, much bigger story!