At the beginning of time, the Big Bang occurred, forming the universe. However, where there should have been one universe, there were many, each one a replication of the first, with their own separate histories.

At the present time, a great white wall of pure anti-matter energy stretches out across the cosmos. It pervades the Multiverse, consuming entire galaxies. On an unknown parallel world, a being named Pariah arrives. He is forced to witness the death of multiple worlds in multiple dimensions. He disappears as he is transported to the parallel world known as Earth-Three. On that world, the Crime Syndicate, in a rare demonstration of heroism, strives to save their beleaguered planet. However, even their combined might cannot prevent their deaths at the anti-matter wall.

The planet's sole hero, Lex Luthor, retreats to his home where his wife, Lois, holds their infant son, Alexander, in her hands. Luthor places Alexander into an experimental rocket capsule and launches him from the planet Earth. As Earth-Three dies, Alexander's capsule pierces the vibrational wall separating dimensions. It lands on the abandoned Justice League Satellite orbiting Earth-One.

On board another satellite, a being called the Monitor summons his assistant Harbinger. He instructs her to travel to various alternate Earths and bring together a select group of super-powered beings. Harbinger uses her power to create replicant versions of herself and sends them to the various Earths. The Monitor meanwhile, prepares to gather Alexander Luthor’s space capsule.

The first of Harbinger's replicants travels to Earth-One and gathers King Solivar from Gorilla City. Another travels to Earth of the 30th century and summons Dawnstar of the Legion of Super-Heroes to her cause. A third replicant journeys to Earth-Two of the year 1942 to enlist the aid of Firebrand. One version gathers the Blue Beetle from Chicago. Another version of Harbinger collects the Psycho-Pirate from Earth-Two's present timeline. She brings him to Earth-One where they encounter Firestorm and Killer Frost. The Psycho-Pirate uses his Medusa Mask to make Killer Frost fall in love with Firestorm. Another replicant travels to Pre-Cataclysmic Atlantis to find Arion the Sorcerer. However, a Demon-Shadow attacks her and takes possession of Harbinger. The possessed replicant finds Arion and brings him back to the Monitor's satellite.

When they arrive, they find a room full of heroes and villains from alternate realities. Before the assemblage has a chance to acclimate itself to their foreign environment, a horde of Demon-Shadows attacks them. They fight them off until the Monitor arrives. He casts a brilliant burst of light, which dispels the shadows. Introducing himself, he tells the impatient gathering that the Multiverse may soon be destroyed.