It was just regular mission at first to stop the Joker, Harley, and his goons... but things didn't end as expected.

Joker had gotten his hands on a new sort of contraption and decided to test it on them, once they stood in a specific area of the warehouse, Harley quickly pulled a lever and they suddenly were surrounded by some sort of electric energy that sent them away by some sort of unknown device.

They tried to prevent it but it was too late, the ground of the city immediately shook violently for several minutes before finally stopping as if nothing had happened p Before they realized that Joker, Harley, and his goons had already run away.

But when returning to the BatCave to track down the Joker again, suddenly the Batcomputer detected the appearance of an unknown city outside Gotham.