In the 1984 film Supergirl, Kara Zor-El (played by Helen Slater) is sent from her home planet of Krypton to retrieve the Omegahedron, a powerful energy source that can keep her people alive. But the Omegahedron is lost in space and eventually ends up on Earth.
Kara follows the Omegahedron to Earth and assumes the identity of Linda Lee, a student at a girls' school. She tries to blend in with the other humans while searching for the orb. Along the way, she discovers her own powers and becomes the superhero Supergirl.
At the same time, the Omegahedron is found by a witch named Selena (played by Faye Dunaway). Selena sees the Omegahedron as a source of power that will allow her to control the world. She uses her magic to manipulate those around her, including a handsome gardener named Ethan (played by Hart Bochner), who becomes infatuated with Linda and eventually finds out her true identity.
As Supergirl, Kara takes on Selena and her minions in several battles, using her strength and abilities to thwart their plans and protect the people of Earth. In the end, Supergirl secures the Omegahedron and returns it to Krypton, restoring power to her home planet and fulfilling her mission.