Plot
In Earth 49, the Joker tricks Superman into killing a pregnant Lois Lane, which subsequently detonates a nuclear weapon that destroys Metropolis. A grief stricken Superman breaks into the Joker's interrogation room while he is being questioned by Batman, and kills him after the former mocks Lois's death. Following the Joker's death, Superman establishes the One Earth Regime, while Batman forms the Insurgency to counteract him.
In the Prime DC universe, the Justice League and Teen Titans subdue various villains across Metropolis and the Watchtower. Batman learns from Lex Luthor that Joker plans to detonate a nuclear weapon in Metropolis. As the Justice League attempt to stop the weapon from detonating, Batman and the Joker are inexplicably teleported to Earth 49, where they escape Regime forces. Wonder Woman, Aquaman, Green Arrow, and Green Lantern are teleported to a different area of the universe, and split up to determine the cause of their arrival. While recharging his power ring, Green Lantern saves a captive Deathstroke from Cyborg and Raven, and rescues Wonder Woman and Green Arrow from Sinestro and his own Yellow Lantern counterpart, who have all joined the Regime.
In Atlantis, Aquaman learns that in the five years following the Joker's death and the establishment of the One Earth Regime, Superman has ruled the Earth as a ruthless dictator, alongside other heroes and villains who support the regime. Upon learning of the Regime's plan to take over Atlantis, Aquaman fights Shazam, Flash, and his own counterpart before being saved by Ares, who has been significantly weakened by the virtual lack of conflict and has allied himself with the Insurgency.
Upon regrouping, Wonder Woman, Green Arrow, Green Lantern, and Aquaman meet Earth 49 Batman and a heroic variant of Lex Luthor, who has become an Insurgency informant while retaining friendly relations with the Regime. Green Arrow receives a nanotech pill derived from Kryptonian DNA, which increases his strength to Superman's level. Earth 49 Batman and Lex Luthor inform the Prime Earth heroes that they had teleported them to Earth 49 to retrieve a Kryptonite weapon that could potentially weaken Superman. However, to access the weapon, Batman needs the DNA of the core Justice League members, who are either deceased or have joined the Regime. In Gotham City, Prime Earth Batman is captured by the Regime, who have learned of the Prime Earth heroes, while Joker meets Earth 49 Harley Quinn, who has joined the Insurgency and founded the Joker Clan in his memory.
After helping the Joker Clan fight off a Regime attack at Arkham Asylum, the Insurgents infiltrate the Batcave and retrieve the Kryptonite weapon while fighting off various Regime members. However, Earth 49 Black Adam damages the weapon while attempting to subdue them, rendering it useless. In the Prime universe, Superman and Flash's efforts to recover the heroes results in Cyborg being inadvertently teleported into the Regime's universe, where he regroups with the Insurgency and helps Deathstroke take over the Regime Watchtower.
After Earth 49 Superman publicly announces his intention to execute Prime Earth Batman, Earth 49 Batman and Green Arrow break into Stryker's Island to rescue him, while Wonder Woman, Green Lantern, and Aquaman distract the Regime. After saving Prime Earth Batman, Earth 49 Batman is confronted by Superman, who lambasts him for going against the Regime. Prime Earth Batman, Earth 49 Batman, and Green Arrow use the Watchtower's teleporter to escape, and Superman flies to the Watchtower in an attempt to capture them. However, Deathstroke detonates multiple explosives inside of the Watchtower that destroys it and sends Superman flying back to Earth. Elsewhere, Lex Luthor retrieves a variant of the Kryptonite weapon and fights Harley Quinn, Joker, and various Regime members. Lex attempts to use the weapon to subdue the weakened Superman but is severely wounded by Shazam. Before being killed by Superman, Lex mocks the Regime's hypocritical methods for achieving peace. Shortly after killing Lex, Superman is overwhelmed by the voices of various civilians who criticize him for murdering Lex.
Now aware of humanity's hatred for the Regime, Superman decides to destroy Gotham City and Metropolis and invade the Prime Earth as revenge for their decision to aid the Insurgency. Shazam protests the plan but is killed by Superman after he mentions Lois. Shocked by Shazam's death and disillusioned with the Regime's brutal methods of achieving peace, Earth 49 Flash defects from the Regime and joins the Insurgency, where he informs them of Superman's plans shortly before the hideout is ambushed by the Regime. During the ensuing fight, Wonder Woman is teleported to Themyscira by Ares, who informs her of Earth 49 Wonder Woman's plan to use Amazonian warriors to invade Metropolis and Gotham City. After defeating Raven and her Earth 49 counterpart, Wonder Woman persuades the Amazonian warriors to join the Insurgency's attempts at pushing back the regime.
As the Prime Earth heroes and Earth 49 Flash attempt to push back the Regime in Gotham City and Metropolis, Prime Earth Batman convinces a reluctant Earth 49 Batman to bring Prime Earth Superman to Earth 49. Upon regrouping with the Insurgency, Prime Earth Superman subdues Black Adam and Sinestro and convinces Yellow Lantern to surrender his ring. Superman and Prime Earth Wonder Woman push back Aquaman's Atlantean forces with the help of the Amazonian warriors, shortly before Superman is attacked by Doomsday, with the former managing to throw the latter into the Phantom Zone during the ensuing fight in the Fortress of Solitude. Prime Earth Superman is confronted by Earth 49 Superman, who announces his intention of wiping out the Prime Earth heroes and bringing Prime Earth Lois to Earth 49. Prime Earth Superman argues that Lois would be horrified at the tyrant Earth 49 Superman would become, leading to a fight between both Supermans. Prime Earth Superman subdues his Earth 49 counterpart, and the Prime Earth Justice League and Earth 49 Batman arrive to arrest Earth 49 Superman. A despondent Earth 49 Superman attempts to convince Batman to kill him, but Batman refuses and instead arrests him.
Following Earth 49 Superman's arrest, the Regime is disbanded, and the members are imprisoned for their crimes. Before returning to Prime Earth, Prime Earth Superman and Earth 49 Batman discuss Batman's plan to bring back freedom and order to Earth. Superman laments that he could've become like his Earth 49 counterpart should the Joker's attempt at detonating the nuclear weapon succeeded. As the two leave, Earth 49 Superman's eyes glow red as he lies in the Red Sun prison.
