Plot
In the 853rd century, the original Superman ("Superman-Prime One Million") still lives, but has spent over 15,000 years in exile within his Fortress of Solitude, located at the heart of the Sun, to keep it alive. During this time of absence, everyone he knew and loved died. One of his descendants is Kal Kent, the Superman of the 853rd century.
The galaxy in the far future is protected by the Justice Legions, which were inspired by the 20th-century Justice League and the 31st-century Legion of Super-Heroes, among others. Justice Legion Alpha, which protects the Solar System, includes Kal Kent and future analogues of Wonder Woman, Hourman, Starman, Aquaman, the Flash, and Batman. Advanced terraforming processes have made all the Solar System's planets habitable, with the ones most distant from the Sun being warmed by Solaris, a "star computer" which was once a villain, but was reprogrammed by one of Superman's descendants.
Superman-Prime announces that he will soon return to humanity and, to celebrate, Justice Legion Alpha travels to the late 20th century to meet Superman's original teammates in the JLA and bring them and Superman to the future.
Meanwhile, in Russia, Vandal Savage single-handedly defeats the Titans (Arsenal, Tempest, Jesse Quick and Supergirl) when they attempt to stop him from purchasing nuclear-powered Rocket Red suits. He then launches four Rocket Red suits (with a Titan trapped inside each of the four) in a nuclear strike on Washington D.C., Metropolis, Brussels, and Singapore.
Starman is bribed into betraying his teammates by Solaris, which has returned to its old habits. Before the original heroes can be returned to their own time, the Hourman android collapses and releases a virus programmed by Solaris. The virus affects the guidance systems of the Rocket Red suits and causes one of them to detonate over Montevideo, killing more than one million people. Tempest escapes, but blacks out and falls into the sea. Believing that this was deliberately planned by the JLA to stop him, Savage launches an all-out war on superhumans.
The two JLAs stop after discovering that discovered that it is a complex computer program looking for appropriate hardware. To provide this hardware, the heroes are forced to build the body of Solaris in the present day. In a final act of repentance, Starman sacrifices himself to banish Solaris from the Solar System. The future Superman forces himself through time using confiscated time travel technology.
Solaris, in a final attack, slaughters thousands of superhumans so that it can fire kryptonite into the sun and kill Superman-Prime before he emerges. The JLA's Green Lantern causes Solaris to go supernova and he and the 853rd century Superman contain the resulting blast, but not before the kryptonite is released.
The future Vandal Savage teleports from Mars to Earth using the stolen Time-Gauntlets. However, Chronos and Resurrection Man (an immortal who had become Savage's greatest foe through the millennia) have sabotaged the Gauntlets so that Savage, instead of travelling only in space, also travels through time. He arrives in Montevideo moments before the nuclear blast, which kills him.
In the aftermath, the original Superman and the future Hourman use the DNA sample to recreate Lois Lane, giving her superpowers. Superman then also recreates Krypton, along with all its deceased inhabitants, in Earth's Solar system.
