With Washington, D.C. in the hands of The Omega Man and the full extent of his horrific power revealed, the JLA is forced to make a difficult decision. Is there no choice for the World's Greatest Heroes but to team with the World's Worst Villains – the Crime Syndicate – in order to save both Earths? How will this desperate action be affected by Ultra Man's betrayal of everyone. . . and the reappearance of Dark Supergirl?