In the year 2862, history professor Kristen Wells conducts a class on the mystery of Superwoman. The mysterious Superwoman was a late 20th Century super-heroine whose secret identity remains unknown, even in Wells' time. After watching videos of Superwoman's feats, Wells' class postulates that all of Superwoman's powers could easily be duplicated by current technology. When Wells asks how Superwoman could possibly have gained access to future technology, her class proposes that Wells take a field trip to the 20th Century to find out. Wells visits the bullpen of the Daily Planet, and gets herself hired on as Lois Lane's typist. Upon laying eyes on Wells, Jimmy Olsen immediately begins hitting on her. Clark Kent, having encountered Wells once before, takes her aside to find out why she's come back to his century.
During their discussion, Kent's super-hearing picks up the arrival of an alien craft in Metropolis. Wells informs Kent that the ship is piloted by King Kosmos, a brutal alien dictator. Kent, as Superman, flies out to confront King Kosmos. Superman comes under fire from King Kosmos' powerful laser cannons. Having discovered Superwoman's costume in Lane's office, Wells confront's Lane, stating that Superman needs her. Lane tells Wells that the costume actually belongs to Kent's cousin, Linda Danvers. Wells attempts to reach Danvers by phone, but Danvers is already en route to Metropolis. Superman finds the fortitude to resist the power of the laser cannon, fighting the pain until he's almost reached the ship. Just as he makes contact with the cannon, the Man of Steel seems to shatter, his body scattered across the skies of Metropolis.
Wells is stunned, as Superman's death at the hand of King Kosmos is not historically accurate. Suddenly, Kent walks in on Wells. Kent reveals that King Kosmos' weapon actually hurled Superman back in time, to Medieval England. To Olsen's chagrin, Kent and Wells head out together. Wells fills Kent in on King Kosmos' history. Wells points out a young girl who is about to race into traffic. With no time to change into his Superman costume, Kent is forced to save the girl in his civilian identity. That night, Wells, on Olsen's invitation, attends a costume party for the Daily Planet staff. King Kosmos creates the illusion of a nuclear attack on Metropolis to draw Superman out. Superman investigates, only to discover the illusion. Suspecting a trap, Superman returns to the party.
King Kosmos tracks Superman to the party, then targets the building with a weapon that instantly fells Superman, as well as all the other partygoers. Only Wells remains standing, having used technology from her time to shield herself from King Kosmos' weapon. Danvers is also among the fallen. Wells suddenly realizes that it is she, herself, who is Superwoman. Donning the Superwoman costume, and outfitting it with her future technology, Wells, as Superwoman, flies out to confront King Kosmos. Responding to the threat of King Kosmos, The Flash, Green Arrow, Wonder Woman, Batman and Robin are all en route to Metropolis, when King Kosmos fells them all. Superwoman phases through the hull of King Kosmos' ship, and commandeers his communications array to issue a defiant speech on behalf of America.
Unimpressed, King Kosmos strikes Superwoman down. King Kosmos launches a nuclear reactor at Dallas, Texas, then departs, leaving Superwoman to fall to her death. A recovered Superman rescues Superwoman. Leading Superman to Dallas, Superwoman has Superman intercept the reactor, before sending the Man of Steel into deep space. There, Superman safely destroys the reactor. Superwoman pursues KIng Kosmos through time, leaving a message for Superman to follow. King Kosmos travels back to the American Civil War to sow chaos. Superwoman tackles King Kosmos, phasing them both out of his ship. King Kosmos, however, manages to keep hold of a remote control unit, allowing him to activate the ship's weapons, and fire on the civilian populace. Superman arrives and disables the ship's weapons.
King Kosmos traps Superman in a pocket of space, one located in a Red Sun system. Superwoman frees Superman, then they both pursue King Kosmos into the time stream. Though Superwoman reaches KIng Kosmos first, she refuses to engage him, only willing to destroy his chronal navigator. Superman battles against King Kosmos, who ultimately flees. Without his chronal navigator, though, he is forever lost in the time stream. Superwoman reveals that she held back because history says Superman, not Superwoman, defeated King Kosmos. Back at the Daily Planet, Kent brags to Olsen, and Lane, that he conducted an exclusive interview with Superwoman. Kent is saying goodbye to Wells, when Olsen makes one last play for her. Wells amorously kisses Kent in front of Olsen, emasculating the young reporter. Wells returns to her time to write up her historical account on Superwoman. When questioned by a student why Wells treated Olsen so cruelly, Wells replies that she had to keep her distance from Olsen, as she is descended from him