The story begins in Gotham decades ago. The Waynes actually had a son. It was rumored that the eldest son had died in infancy - Thomas Wayne Jr. Although the doctor told the Waynes when they saw the baby that the child had died prematurely, no one knew that the doctor was from the Court of Owls and that the dead Thomas had actually been taken away.
The Justice League received a clue that there was a place where the Court of Owls was based. When the group finally got to the location with Batman's consent, what they saw in front of everyone was a man soaked in a green pool. And that person looks exactly like Bruce Wayne, and this pool is not an ordinary pool...
Purpose: To fulfill the wish of an owl in the next universe