In the year 2865, Superwoman serves as Grand Marshall at an Independence Day festival. After leading the celebration, Superwoman decides it's finally time to return to the 20th Century, to live out her legend. In 20th Century Metropolis, Greg Reed, an actor famous for portraying Superman, is nearly killed in a car accident. Only the quick action of the real Superman saves Reed's life. Kristen Wells journeys back to the 20th Century, unaware that a bureaucratic error accidentally sent her through a time vortex, instead of a time warp. As a result, Wells arrives in the 20th Century with no knowledge of who she is, or why she is there. Her future attire leads a passerby, on the street, to suggest she attend Luthorcon III, a convention honoring Superman's arch-nemesis, Lex Luthor.
Superman is also in attendance at Luthorcon, masquerading as Reed, who was to perform, in his role as Superman, at the convention. Wells, having discovered her Superwoman uniform, attends the convention in costume. Unbeknownst to the convention attendees, they are under observation by Lex Luthor. Superman, as reporter Clark Kent, covers the convention, for the nightly news. Kent is overcome by a sudden weakness, when one of the food vendors passes by him. Seeing Kent, Wells begins to remember bits of her past, including her name and occupation. Lost in her reverie, Wells is struck from behind, by the food vendor. Kent's super-hearing alerts him to the potential collision of an oil tanker and a whale, in the Metropolis river.
Making an excuse to duck out, Kent, as Superman, rescues the whale, carrying it out to sea. As he passes over the conventioneers, the whale sprays them all down with river water, expressed from it's blowhole. Remembering that she once worked at the Daily Planet, Wells wanders in to the bullpen. Back at Luthorcon III, Superman, pretending to be Reed, takes part in a mock Kryptoniting of Superman, at the hands of three conventioneers, dressed as Lex Luthor. The Kryptonite, though, is real. Superman tries to convince the "Luthors", and the audience, that he's in real distress, but all believe it's merely part of the show. Having garnered no answers at the Daily Planet, Wells returns to the streets of Metropolis.
Witnessing a museum robbery, Wells intervenes, as Superwoman. Having easily defeated the thieves, Superwoman returns to Luthorcon III. Seeing Superwoman in the audience, Superman's pleading eyes convince her to dispose of the Kryptonite. His powers rapidly returning, Superman and Superwoman take to the skies together. Luthor threatens to project Metropolis into a hostile dimension, unless Superwoman recovers the Kryptonite, and re-exposes Superman to it, until he dies. To add emphasis to his threat, Luthor shatters a bridge. While Superwoman rescues the motorists on the bridge, Superman repairs it at super-speed. Superwoman flies into space to retrieve the Kryptonite.
Superman goes on the air to announce his compliance with Luthor's demands. However, Superwoman returns without the kryptonite. Luthor uses a time vortex to displace Metropolis. Superman and Superwoman are hard pressed to keep the damage to the city minimal, and make sure no lives are lost. Somehow, Superwoman has altered the time vortex's trajectory so that it, ultimately, displaces Luthor, returning Metropolis to it's proper place in space and time. With her memories fully returned to her, Superwoman remains in the 20th Century, to perform the heroic deeds recorded in the history books of her time. Once she reaches the end of those amazing adventures, Superwoman returns to her native time. Wells retires her costumed identity to live out the rest of her life as a history professor.