Plot
In the year 2987, R.J. Brande, the galaxy's richest man and head of Brande Industries, discovers a life pod in an asteroid belt containing Kal-El of Krypton, who had crashed in it after being sent to Earth one thousand years ago before Krypton's destruction. Brande adopts Kal, who takes the name Kal Brande, gaining superpowers from Earth's sun and calling himself Superboy. Inspired by legends of superheroes from the 20th century, he uses his powers to help humans.
Every planet in the Milky Way Galaxy is protected by the Science Police, who are guided by the supercomputer Universo. The Science Police sees Kal as a misfit because he damages public property and makes unregistered flights, and threatens R.J's business if he does not control Kal's behavior. After a heated argument with Brande, Superboy flies off into space to the former location of Krypton and meets Talu-Katua, a member of the Green Lantern Corps who inspires him to form his own group.
Meanwhile, on the luxury space cruiser Lystrata, a young couple, Imra Ardeen, a psychic, and Rokk Krinn, who has magnetic abilities, help defend the ship against an energy being and are helped by Superboy. The trio form a team called Superboy's Legion. Imra calls herself Saturn Girl, and Rokk calls himself Cosmic Boy. They hold televised tryouts, covered by young reporter Lois Olsen, for more members on Titan. They induct best friends Dirk Morgna (Sun Boy) and Gim Allon (Colossal Boy), Salu Digby (Shrinking Violet), Chuck Taine (Bouncing Boy), Jan Arrah (Element Lad), and Tasmia Mallor (Shadow Lass). Superboy meets Lois and a spark seems to form between the two after the tryouts. When news comes of a giant asteroid about to collide with planet Rimbor, the Legion sets out to save the planet.
As the Legion heads for Rimbor, Lyle Norg (Invisible Kid) and Querl Dox (Brainiac 5) inform them that their plan to smash the asteroid will fail because the asteroid is too large. The Legion calls in Thom Kallor (Star Boy), the last survivor of the planet Xanthu, who uses his gravity powers to increase Superboy's mass to stop the asteroid. Superboy shatters the asteroid, and the Legion collects the fragments.
The Legion is attacked by the Fatal Five, five of the most dangerous criminals in the galaxy and the ones responsible for Xanthu's destruction. In the battle, Mano burns Star Boy's face with his antimatter touch, Persuader cuts off Cosmic Boy's arm with his axe, and Validus kills Colossal Boy. When the Five leave, they take Brainiac 5 with them under orders from their leader, Lex Luthor.
Superboy is not sure he wants to do any more good, after getting Colossal Boy killed, but Star Boy encourages him to rescue Brainiac 5. The rescue party arrive at Colu, but the planet is now visible and is being accessed by the computers in Luthor's ship. Luthor sics the Fatal Five on the heroes to avoid interference. Superboy and the Legion arrive and incapacitate the majority of the villains. Sensor mind controls Emerald Empress into believing her Eye has been destroyed. Tinya and Reep trick and knock out Mano and the Persuader, and Sun Boy stops Validus.
On Earth, Saturn Girl senses a malevolent presence inside Universo and attempts to find it, but Commissioner Leeto orders the Science Police to gun her down. The Science Police realize Leeto is paranoid, and sees Saturn Girl is their only hope as Universo starts to crash. Saturn Girl discovers the evil presence is diverting Universo's power to Colu. Luthor becomes aware of the interference and snaps Emerald Empress out of Sensor's illusion to stop Saturn Girl. Emerald Empress arrives on Earth and traps Saturn Girl and the others, but Ferro Lad and Karate Kid incapacitate the Emerald Eye and Empress, respectively, and Saturn Girl befriends the Eye, convincing it to serve as Universo's replacement.
On Colu, Superboy rescues Brainiac 5 from Luthor's ship, but Luthor has transferred his mind into an indestructible robot and continues to hack into Colu. After the Legion rescues him from Tharok, Superboy engages Luthor, who reveals he plans to transfer his mind into Superboy's body to achieve immortality. The Legion severs his link to Colu, and Brainiac 5 forces Luthor to face the truth—that he is a computer and the original Luthor has been dead for centuries, hidden inside Universo. Furious at this revelation, Luthor decides to destroy himself and Colu, though Superboy and Ultra Boy are able to save both. The Coluans teleport the Legion's friends and R.J. Brande to Colu and Superboy makes up with his adoptive father. Subsequently, the Legion become the official heroes of the newly formed United Planets. Superboy hands over leadership of the Legion to Ultra Boy, renames himself Kal-El and starts dating Lois Olsen.
