In this captivating spin-off from the acclaimed Superman franchise featuring Christopher Reeve, we follow the adventurous journey of Kara Zor-El (played by Helen Slater), a teenager living in the Kryptonian enclave of Argo City. This remarkable city was mysteriously transported into another dimension known as "inner space" following the catastrophic explosion of planet Krypton many years prior. The lifeblood of Argo City is powered by a small yet powerful orb called the Omegahedron.
One day, a curious resident named Zaltar (portrayed by Peter O'Toole) takes a bold risk by borrowing the Omegahedron for an art project. Unfortunately, a blunder results in the orb being sent into the vastness of space. Without the Omegahedron, Argo City faces imminent destruction, prompting Kara to embark on a daring mission to retrieve it despite the grave concerns of her parents, Alura (played by Mia Farrow) and Zor-El (Simon Ward).
The Omegahedron is eventually drawn through a wormhole, landing unexpectedly on Earth, where it is discovered by Selena (brought to life by Faye Dunaway), a fortune teller with grand aspirations of becoming a witch. Selena, having long studied magic under the tutelage of the warlock Nigel (Peter Cook), recognizes the orb's potential to enhance her magical abilities and hides it away. Returning to the carnival, her worried assistant, Bianca (played by Brenda Vaccaro), frets over their financial struggles, but Selena assures her that their monetary worries are over, ominously hinting at her plans for "world domination."
Simultaneously, Kara is transported to Earth and transformed into Supergirl, donning a costume that resembles that of her cousin, Superman, who is away on a peacekeeping mission in outer space. Discovering her newfound superpowers, Kara is exhilarated as she explores the wonders of Earth. A glowing bracelet warns her of the Omegahedron's presence, guiding her to Midvale, Illinois. There, she enrolls in an all-girls school and introduces herself as Linda Lee, claiming to be the orphaned cousin of Clark Kent.
At school, she becomes roommates with Lucy Lane (Maureen Teefy), the spirited sister of Daily Planet reporter Lois Lane. Both Selena and Bianca soon find themselves smitten with a handsome groundskeeper named Ethan (Hart Bochner). In a fit of jealousy, Selena brews a love potion to ensnare Ethan’s heart. However, the potion backfires, leaving him in a daze instead. With a little help from the Omegahedron, Selena commands a bulldozer to transport Ethan to her, but chaos ensues as the machine careens wildly through town.
In a heroic turn, Kara dons her Supergirl persona and halts the rampaging bulldozer, transforming back into Linda Lee just in time for Ethan to awaken and be enchanted by her. Furious at this turn of events, Selena vows to gain revenge and, using her dark magic, aims to trap Linda. As clouds of shadows loom, Linda shifts into Supergirl, boldly facing the storm where she triumphs by conducting a lightning rod with a streetlamp to deter Selena's attack.
Determined to confront Selena, Kara discovers Ethan at the carnival, and they share a sweet moment amidst the chaos, but Selena interferes by sending their carnival ride into a frenzy. The time has come for Supergirl to confront Selena directly, trapping her in a makeshift cage while rescuing Ethan from danger.
But the escalating battle leads Selena to summon her master, Nigel, for aid as they craft powerful magic together. Their combined forces inadvertently undo the love potion, leaving Ethan to forget Linda but soon, he finds himself drawn to Supergirl instead. As Selena casts a spell to imprison Ethan in her lair atop a mountain, Supergirl is banished to the Phantom Zone, where she reunites with Zaltar, who had exiled himself there in remorse.
Though without powers in the Phantom Zone, Supergirl, inspired by Zaltar's insistence, seeks a way out, climbing treacherous cliffs to freedom. Back on Earth, Selena's ambitions spiral out of control, commanding the town with a fearsome display of power.
In a dramatic showdown, Supergirl returns from the Phantom Zone just in time to confront the demon that Selena conjured. With Zaltar’s encouragement echoing in her spirit, she channels her strength and sacrifices her focus to turn the demon against its master, engulfing Selena, Bianca, and the demon in a magical whirlwind that exiles them to the Phantom Zone forever.
At last, Ethan retrieves the Omegahedron and recognizes the duality of Supergirl and Linda Lee. As she prepares to return the orb, Supergirl impresses upon Ethan, Lucy, and Jimmy the importance of keeping her identity a secret. With the Omegahedron in hand, she flies back to Argo City, where the city begins to shine again, bringing hope and vitality back to her homeland.
