Plot
The conglomerate Webscoe Industries hires computer programmer Gus Gorman, who secretly embezzles $85,000 from the company payroll. He comes to the attention of Webscoe's CEO, Ross Webster. A cunning billionaire fixated on using technology for financial domination, Webster sees Gus's skills as a valuable asset. With the help of his stern sister, Vera, and his mistress Lorelei Ambrosia, he blackmails Gus into aiding his schemes.
Clark Kent, accompanied by Jimmy Olsen, returns to Smallville for his high school reunion. Along the way Clark—as Superman—extinguishes a fire in a chemical plant. Jimmy is injured during the fire and is taken to hopsital. In Smallville, Clark reconnects with childhood friend Lana Lang, who has a young son named Ricky. Superman later saves the boy from a combine harvester during a picnic with Lana.
Webster orders Gus to use the weather satellite 'Vulcan' to create a storm that destroys coffee crops in Colombia, aiming to corner the market. Gus complies, but Superman neutralizes the storm. Recognizing the hero as a threat, Webster orders Gus to synthesize Kryptonite. When the computer fails to recognize the total chemical composition, he substitutes tar for the unknown elements. Lana invites Superman to Ricky's birthday party. Gus and Vera infiltrate the party, giving Superman the synthetic Kryptonite, which leaves him unharmed, to their confusion. Instead, he gradually becomes corrupted after exposure to it, committing sophomoric acts such as straightening the Leaning Tower of Pisa and blowing out the Olympic Flame.
Gus proposes building a supercomputer for Webster in exchange for creating an energy crisis by redirecting oil tankers. Lorelei seduces Superman and manipulates him into causing an oil spill. Superman suffers a nervous breakdown and splits into two beings: the corrupted Superman and Clark Kent. The two fight, and Clark defeats his corrupted counterpart by strangling him to death. The renewed Superman then repairs the damage from the oil spill. After surviving exploding rockets and a missile, Superman confronts Webster, Vera, and Lorelei in the supercomputer. The computer becomes self-aware and defends itself against attempts to disable it as it transforms Vera into a cyborg. Vera then attacks Webster and Lorelei with energy beams that immobilize them. Superman retrieves a can of acid from the chemical plant and uses it to destroy the computer. Superman hands Webster, Vera and Lorelei to the authorities. Gus starts anew in West Virginia.
Meanwhile, Clark visits Lana in Metropolis, where she begins working as a secretary for Perry White. Lois Lane returns from Bermuda with an exposé on corruption, and Superman restores the Leaning Tower of Pisa before flying into space.