As the planet Krypton is on the verge of exploding, Jor-El and Lara put their newborn son Kal-El in a spaceship bound for Earth. An alien parasite named Starro escapes his containment in Jor-El's lab and stows away on the ship before it is sent to Earth but falls off the ship shortly partway through its journey. The spaceship lands in Kansas where Kal-El is raised by Jonathan and Martha Kent, and named Clark. Clark discovers he has superhuman abilities and becomes Superman. He meet Batman and reveals his identity to Lois Lane; the two marry and have a son named Jon.
Years later, the Kents are living in Smallville. Jon is frustrated by his father's frequent absences unaware that Clark is Superman. One night, Superman saves the Justice League Watchtower from falling out of orbit after it is impacted by space debris. Superman has to leave to save Japan from a tsunami. On the Watchtower, Green Arrow is attacked by a creature.
The next day, at his birthday, Jon develops heat vision. Clark reveals that he is Superman and takes Jon to Gotham City to see Batman for advice on when or if the rest of Jon's powers could emerge. Jon meets Batman's son Damian Wayne aka Robin who is initially rude to him. Batman reveals to Superman that he has lost contact with the Watchtower and the two depart for the Watchtower to see what is going on after Superman drops Jon off back in Smallville. When Batman and Superman arrive at the Watchtower, a possessed Martian Manhunter infects them with Starro spores.
Returning to the Batcave, the possessed Batman attempts to infect Damian but the boy slices the spore apart. After Damian tricks Batman's spore into thinking that it has successfully killed him, he overhears that Starro has been able to infect both the Justice League and Teen Titans and intends to infect Jon next. Damian travels to Smallville where he and Jon escape an infected Lois. Jon uses his heat vision on the Starro spore infecting Lois which frees her from Starro's control. Damian and Jon travel to the Fortress of Solitude to use its Kryptonian technology to analyze a fragment of the Starro spore intended for Damian. After being mistaken for intruders by Krypto, they meet a holographic copy of Jor-El's consciousness. Jor-El explains that the Starro spores are being controlled by a central hive-mind Starro. Jon and Damian realize that Starro is on the Watchtower and if they take it out, it will free everyone who is under control by a spore.
Jon and Damian travel to the Watchtower in the same ship that brought Kal-El to Earth. On the Watchtower, they are apprehended by possessed members of the Justice League and the Teen Titans. Starro explains that he intends to drain the Earth of life after securing control over everyone. Jon's invulnerability manifests when he jumps in front of an arrow fired by the possessed Green Arrow at Damian and the duo is able to subdue the possessed heroes attacking them. Lois is able to contact Jon from President Lex Luthor's office and tells Jon that Starro is vulnerable to heat. They discover that Starro has grown stronger and Jon's heat vision is no longer enough to destroy him. They resolve to knock the Watchtower out of orbit in the hopes that Starro will burn up with it on re-entry.
After evacuating all of the subdued heroes on spacecraft back to Earth, they are able to set the Watchtower on a course for re-entry. They are attacked by Starro, but he is injured as the Watchtower begins to burn up on re-entry which causes all Starro spores on Earth to die. Unable to escape from the Watchtower, Damian and Jon admit their respect for each other. Freed from Starro, Superman intercepts the falling Watchtower and rescues Jon and Damian. Starro survives the fall to Earth where he is defeated by Jon, Damian, Batman, and Superman working together.
Afterwards, Damian and Bruce visit the Kent family in Smallville. Jon and Damian discuss a name for themselves before settling on Super-Sons.
Years later, the Kents are living in Smallville. Jon is frustrated by his father's frequent absences unaware that Clark is Superman. One night, Superman saves the Justice League Watchtower from falling out of orbit after it is impacted by space debris. Superman has to leave to save Japan from a tsunami. On the Watchtower, Green Arrow is attacked by a creature.
The next day, at his birthday, Jon develops heat vision. Clark reveals that he is Superman and takes Jon to Gotham City to see Batman for advice on when or if the rest of Jon's powers could emerge. Jon meets Batman's son Damian Wayne aka Robin who is initially rude to him. Batman reveals to Superman that he has lost contact with the Watchtower and the two depart for the Watchtower to see what is going on after Superman drops Jon off back in Smallville. When Batman and Superman arrive at the Watchtower, a possessed Martian Manhunter infects them with Starro spores.
Returning to the Batcave, the possessed Batman attempts to infect Damian but the boy slices the spore apart. After Damian tricks Batman's spore into thinking that it has successfully killed him, he overhears that Starro has been able to infect both the Justice League and Teen Titans and intends to infect Jon next. Damian travels to Smallville where he and Jon escape an infected Lois. Jon uses his heat vision on the Starro spore infecting Lois which frees her from Starro's control. Damian and Jon travel to the Fortress of Solitude to use its Kryptonian technology to analyze a fragment of the Starro spore intended for Damian. After being mistaken for intruders by Krypto, they meet a holographic copy of Jor-El's consciousness. Jor-El explains that the Starro spores are being controlled by a central hive-mind Starro. Jon and Damian realize that Starro is on the Watchtower and if they take it out, it will free everyone who is under control by a spore.
Jon and Damian travel to the Watchtower in the same ship that brought Kal-El to Earth. On the Watchtower, they are apprehended by possessed members of the Justice League and the Teen Titans. Starro explains that he intends to drain the Earth of life after securing control over everyone. Jon's invulnerability manifests when he jumps in front of an arrow fired by the possessed Green Arrow at Damian and the duo is able to subdue the possessed heroes attacking them. Lois is able to contact Jon from President Lex Luthor's office and tells Jon that Starro is vulnerable to heat. They discover that Starro has grown stronger and Jon's heat vision is no longer enough to destroy him. They resolve to knock the Watchtower out of orbit in the hopes that Starro will burn up with it on re-entry.
After evacuating all of the subdued heroes on spacecraft back to Earth, they are able to set the Watchtower on a course for re-entry. They are attacked by Starro, but he is injured as the Watchtower begins to burn up on re-entry which causes all Starro spores on Earth to die. Unable to escape from the Watchtower, Damian and Jon admit their respect for each other. Freed from Starro, Superman intercepts the falling Watchtower and rescues Jon and Damian. Starro survives the fall to Earth where he is defeated by Jon, Damian, Batman, and Superman working together.
Afterwards, Damian and Bruce visit the Kent family in Smallville. Jon and Damian discuss a name for themselves before settling on Super-Sons.