It's a race against time for Superman and Mon-El to prevent the lethal forces of Xa-Du and Aethyr from converging! But to save the present, the Man of Steel is forced to face the past! It's the dramatic return of Krypton's last son to his homeworld as the Man of Tomorrow voyages to the City of Yesterday! Plus, Kara meets the being at the center of her quest! What could they have done to cause the whole universe to unite against them? Find out in the next thrilling chapter of Supergirl!