Kara Zor-El, cousin of Kal-El/Superman and Jor-El's niece, lives in Argo City, an isolated Kryptonian community that survived the planet's destruction by being transported into a pocket of trans-dimensional space, the Survival Zone. A man named Zaltar allows Kara to see a unique and immensely powerful item known as the Omegahedron, which he has borrowed without the knowledge of the city government, and which powers the city. However, a mishap leads to the Omegahedron being rocketed into space. Taking a ship, Kara follows it to Earth (undergoing a transformation into "Supergirl" in the process) to recover it and save the city.