For long years, Superman believed himself to be the lone survivor of the planet Krypton. Throughout his life, the Man of Steel worked at assimilating himself into human culture, while never forgetting how truly alone he was. When his cousin arrived on Earth, he rejoiced at having Supergirl with whom to share his long-lost culture. Now, the possibility of a third Kryptonian has arisen, catching the attention of not just Superman, but also Batman and an alien mercenary determined to destroy all vestiges of Krypton"s legacy throughout the galaxy. Superman"s hunt for the Third Kryptonian puts at risk everything he cares about, including a young Kryptonian boy born of his greatest enemy within the Phantom Zone.