Résumé: Years ago and nine million light-years from Earth, the planet Krypton is a society rigidly stratified by class, with the ruling Science League at the top and the Labor Guild at the bottom. All citizens wear the symbol of their caste on their chest. In the Labor Guild's case this is the "Crest of the Laborer", which resembles a stylised "S". Jor-El and Lara Lor-Van are members of the Labor Guild and live in the Redlands, the agricultural hinterlands outside Krypton's great cities. Although both showed great promise in their youth they were blacklisted from the Science League for heterodox opinions: Lara for criticising Krypton's lack of space exploration and Jor-El for warning that the League's pursuit of progress at all costs was damaging the environment and putting Krypton at risk of a planetary catastrophe. For this they were consigned to the Labor Guild: Lara is a farmhand and mechanic and Jor-El is a mining engineer. However, they wear their low status with pride, as the Labor Guild are the last people on Krypton to work with their hands, the "People of Steel".
At the mine where Jor-El works, miners report hearing loud splintering from within a shaft. Although all scans show the shaft as stable Jor-El, as the geotechnical engineer, orders the shaft evacuated and goes down to investigate. A visual inspection reveals nothing but Jor-El insists that more in-depth probing is required before he can deem the shaft safe. The mine manager demands that he reopen the shaft but Jor-El refuses. Suddenly, they are rocked by an earthquake and the shaft begins to collapse around them. The ground under their feet splits open and clouds of green, radioactive gas burst up from below, horribly burning and killing anyone it touches. Jor-El flees for the surface.
In the present day on Earth, at a diamond mine owned by the multinational Lazarus Corp, migrant workers are forced down into the mines. Three days ago they discovered a deposit of asbestos and tried to stop work, but were forced at gunpoint by Lazarus' private army of Peacemaker soldiers to keep digging without safety equipment. This not only endangers their health, but the disturbed asbestos also rises up to the surface and falls on the shantytown where their families live. However, when the workers go down they find that every trace of asbestos is gone and the diamonds have already been mined and processed. One of the miners say they should tell someone, but another named João says they should just take the diamonds to the surface and collect their pay. Another miner asks him if he thinks the fabled "Omega Men" could be behind this, but João tells him to never speak of it.
The previous night, João had invited a mysterious new worker in the camp to join him and his family for an evening meal, telling him it was dangerous to be alone. The man had said he had seen the wonders of "your" world and places like the camp where industries ran on suffering. He had asked João which was the truth and João had replied that when you have something worth fighting for, that is the truth. The man had replied that he had nothing and disappeared, saying he had work to do.
One of the Peacemakers beats João, demanding to know where the diamonds came from. Just as he is about to kill João, one of his men reports that one worker did not show up to his shift. The missing worker is the man João met the previous night: Kal-El, the adult son of Jor-El and Lara, who has been travelling between Lazarus facilities in the developing world for years trying to help their exploited workers. He secretly cleared the mine of asbestos and dug up the diamonds in the night, but was exhausted and overslept when he had intended to sneak away from the camp at first light. His high-tech Kryptonian suit detects the Peacemakers coming towards his shack and wakes him up, then charges him up with solar energy to fuel his powers.
The Peacemakers charge through the camp to Kal-El's shack in an armoured vehicle, with workers scrambling to get out of the way. They surround the shack and order Kal-El to come out and surrender. Instead he charges out at super-speed and smashes their tank. The Peacemakers open fire but their bullets harmlessly bounce off Kal-El. The suit's A.I., known as Sol, tells him that the Peacemaker's weapons and armour incorporate alien technology like other Lazarus Corps forces they have faced and advise him to run; but after years of seeing humanity exploit the poorest and weakest among them Kal-El is ready to fight, simply asking if the Peacemakers will survive if he punches them. When Sol replies that they will Superman leaps into battle against the Peacemakers, saying it's his fault the miners are in danger of being caught in the crossfire and he and won't leave until they are safe. Meanwhile the Peacemakers' guns automatically adjust to fire higher-calibre ammunition when they are unable to hurt him.
Kal-El rounds up some of the workers, including João, at super-speed and apologises for putting them in danger. João recognises Ka-El, and he tells them to take the diamonds and run while he fights the Peacemakers. The Peacemakers attack him with reaper drones that blast him with electricity, temporarily overcoming him with pain. Lazarus' elite Phenomena Field Team, who are inbound, tell the Peacemakers to call off the drones as Lazarus wants him taken alive. However, the drones continue and in desperation Kal-El activates his heat vision, which causes him great pain and he cannot control. He destroys the drones and the explosion knocks the Peacemakers out, but Kal-El can't turn off the heat vision by himself, requiring Sol to do it. Sol once again tells Kal-El to run.
As the miners are escaping into the jungle and Phenomena has just arrived on the scene with air support and tanks, Kal-El agrees they should get out of there. However, a Lazarus agent sneaks up and cuffs herself to him with advanced restraints. The agent, Lois Lane, points her blaster at his head and tells him she will fry him if he moves. At Lazarus Corp's headquarters in Nevada, a mysterious scientist in a lab filled with bottled cities watches the fight on a bank of screens. Meanwhile in Kansas, an isolated farmhouse with a mailbox labelled "Kent" lies abandoned and in ruins, the land having been bought by Lazarus Corp long ago.
Years ago on Krypton, Jor-El returns home with radiation burns on his face. Lara runs out to him and asks him what happened, and Jor-El tells her he fears Krypton is doomed. In a sudden panic he asks where Kal-El is and Kal, a boy of around twelve, walks up and asks what's going on. His parents hug him and promise him they will get through whatever comes together as they always have. Nearby, a vent opens up in the ground and the green gas leaks up from below.