Kara Zor-El lives in an isolated Kryptonian community named Argo City, in a pocket of trans-dimensional space. 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, after a mishap, the Omegahedron is blown out into space. After overhearing the wariness of her parents, Kara follows it to Earth (undergoing a transformation into "Supergirl" in the process) in an effort to recover it and save the city.