Batman: City of Madness #1

During Batman's most recent battle with Two-Face, Batman becomes aware of a third personality within Harvey. Meanwhile, a sinkhole has opened up in Gotham, revealing an entrance to a forgotten buried section of Gotham, where the Court of Owls has imprisoned a dark version of Batman. When Batman Below escapes from his prison, prompting the Court of Owls to want to join forces with Batman to stop the creature.