There is a tear in the fabric of reality in the sky above Gotham

Before Jim could brief Batman on any of the litany of problems plaguing their fair city, the sky crackled overhead. Bruce thought it was merely a thunder crack but there was not a cloud overhead for miles. His eyes widened when they landed on a colossal tear in reality over Gotham.

"Batwing. Now." The jet descended to his location, the dynamic duo hopping inside. "We're going to get a closer look. You may want to have the mayor issue an evacuation if it's dangerous." The cockpit window closed and Batman flew up to the anomaly.

The cerulean blue glow was pulsating, smaller arcs of electricity bouncing off of it. The cockpit opened and Batman stood up from it.

"Bruce? Be careful!" Dick urged him, peaking his head out. Batman's breathing became shallow as he reached towards it. It had to be a portal of some kind. His readings didn't indicate it to be a threat to organic life so he neglected contacting the League

Once Bruce made physical contact with the breach in reality, he and Dick were transported to another dimension where they inhabited new bodies to blend in with that Earth's timeline.