The Enemy Below Part 2
Aquaman’s brother has ousted him, stolen his child, a nuclear submarine from the humans and has staged a war with the surface world. The Justice League tries to intervene but it captured and put in a evil master mind death set up (trapped in a room slowly filling with water where they can’t use their powers, the usual. Maybe it’s a traditional Atlantean execution?)
But The League has unknown allies on the inside, which is good, because Aquaman’s brother plans to kill both Aquaman and his infant son and frame the surface for their deaths, clearing room for him to rule. Now the League has to stop the civil war and the invasion.