University physicist, Ray Palmer, escorts his fiance, Jean Loring, through the woods near Ivy University. Palmer struggles with revealing his secret identity, as the Atom, to Loring. Suddenly, Palmer sees his shadow split into two. Looking skyward, Palmer, and Loring, see two moons in orbit over the Earth. Police scientist, Barry Allen, hears a police bulletin, regarding a robbery, committed by Captain Cold. Allen responds, as the Flash. The Flash quickly apprehends Captain Cold, then notices the twin moons in the sky. The gravitational pull of the new moon begins to create seismic disasters on Earth.
Central City suffers a massive earthquake. Aquaman finds new volcanoes emerging on the ocean floor. Elongated Man deals with a tidal wave threatening Italy. Aquaman, the Elongated Man, and the Flash activate their Justice League of America distress signals. The Red Tornado reports on the situation. The new moon appears to be inhabited. It's presence is causing geophysical disruptions across the Earth. The nations of the world are begging for assistance from the Justice League of America. The Green Lantern, and Superman, fly out to the new moon.
The Red Tornado, and Wonder Woman, transport down to Earth, to offer aid. The Batman tracks Ra's Al Ghul to New Delhi, India. The Batman has to give up the hunt for his nemesis, when earthquakes begin to strike New Delhi. The Red Tornado joins the Batman, in New Delhi. Two aliens, Oregnu and Dorth, break into a nuclear power plant, to steal radioactive material. While the Red Tornado deals with the geophysical upheaval in New Delhi, the Batman confronts the aliens. The Batman attacks Dorth, who disintegrates on contact.
Oregnu converts his body into a beam of sliver light, and escapes. The Justice League of America work across the globe, to keep the damage from the geophysical upheavals to a minimum. The Green Lantern, and Superman, are attacked on the new moon. After defeating the alien forces, the High Governor, Fornag, surrenders. Wonder Woman coordinates the Justice League of America's efforts, across the Earth, from her robot plane. Wonder Woman keeps an iceberg from striking an ocean liner. After Loring has been given a sedative, Palmer goes into action, as the Atom.
The Atom floods Ivy Town, to extinguish all the fires. The Red Tornado contains the force of an eruption within his whirlwinds. The Red Tornado carries that eruption out over the Indian Ocean, where he disposes of it. The effort causes the Red Tornado to collapse into the sea. The Batman rescues the Red Tornado. The Justice League of America fight a losing battle to contain the violent forces being unleashed upon the Earth. Fornag identifies the second moon as "Regna". According to Fornag, Regna has always orbited the Earth, in a different vibratory plane.
Some unknown cataclysm threatened to destroy Regna. Regnan scientists built a transporter that shunted Regna into the Earth's vibratory plane, saving Regna, but placing the Earth in jeopardy. The transporter, however, melted into slag after a single use. As the transporter is made of gold, the Green Lantern cannot use his power ring to repair it. Superman asks to see the transporter's blue prints, so that he can fashion a new one. Fornag readily agrees. Unbeknownst to the two heroes, Fornag has plans being carried out, on the Earth, to wipe out all life on the planet.
The Green Lantern is suspicious of Fornag's story. The Batman tracks Oregnu to an atomic submarine, in Panama. The Batman, and Red Tornado, assist the US Navy in repelling the alien invaders. The Batman, and the Red Tornado, are subdued. Using stolen nuclear material from several different power plants, Oregnu intends to turn the nuclear submarine into a bomb. One that will coat the entire planet in radioactive fallout, killing all life on the Earth. The Batman infiltrates the aliens. The Batman transports backs to Regna, with the aliens.
The Batman steals the detonator for the bomb, then joins up with the Green Lantern, and Superman. Farnag orders the deaths of the three heroes. The Batman, the Green Lantern, and Superman prove more than a match for Regna's entire army. The Green Lantern realizes that Regna didn't come from another dimension, but from Earth's past. Fornag confirms the Green Lantern's findings. Regna was at war with the fifth planet from the sun. Regna destroyed that world, which became the asteroid belt around Mars. The destruction of that world, though, thrust Regna into the 20th century. Superman moves Regna one billion years into the future, when all life on Earth has become extinct. The crisis over, the Justice League of America set about rebuilding the world.