After mistakenly losing the Omegahedron, Argo City's life-sustaining power source, Kara takes off on a mission to Earth to retrieve it and save the city. Upon reaching Earth, she is transformed into Supergirl and carries the alias Linda Lee. She must deal with the evil ambitions of a wicked witch, Selina (Faye Dunaway), and her meddling ex-boyfriend Nigel, who plan on ruling the Earth with help from the power of the Omegahedron, which they found when it crashed landed on Earth. Assisted by Jimmy Olsen and Lucy Lane, Lois Lane's sister, Supergirl is off on an adventure to save the Earth and Argo City.