Harley's on to the next stop on her quest to find out how the Joker is haunting her from beyond the grave-and that's the 51st state of Atlantis! Sure, the city under the sea is all Starbucks and water-logged hipsters now, but since Aquaman was the last person to see the Clown Prince alive, can the King of the Sea provide Harley with some much-needed answers? And will they come in time before the Laughing Boys make their ultimate move?