Ocean Master and Black Mantra emerge from the ocean to declare war against the surface as a result of the events that occurred in "Justice League: War" which caused the death of their king. Queen Atlanna looks for her other son, the half-brother of Ocean Master. He is half-human and has aquatic powers but does not know about his Atlantean background. Queen Atlanna believes he can restore balance. He ultimately joins the Justice League and helps them fight to save the Earth.
