by DC Crisis On Infinite Earths, was DC Comics attempt to clean up years of stories, into one streamlined Earth/Universe. This series also brought in characters that DC Comics had aquired from other companies, such as Blue Beetle, Question, Capt. Atom, Peacemaker, Nightshade (Charlton Comics).
Everything starts out with a mysterious figure known as Pariah. He is the witness of universe after universe being destroyed. He sees the Universe with Earth-3 disappear. Even the Criminal Syndicate and Alexander Luther Sr. are unable to stop its destruction. Alexander Luther Sr. and his wife Lois know that they can not stop the destruction of their universe so they send their son Alexander Luther Jr. to another dimension in hopes of saving his life. The pod with Luther Jr. goes to the universe of Earth-3.
Lyla and the Monitor watch as universe after universe is destroyed. In an attempt to stop the end of existence Monitor sends Lyla as the Harbinger to find the one the Monitor has selected to save it. Harbinger separates into multiple selves and takes off to multiple universes and times. She summons King Solavar from Earth-1's Gorilla City, Dawnstar from Earth-1's future, the first Superhero known as Firebrand from Earth-2's past in WW II, and the Azure Avenger Blue Beetle from Earth-4. One of her forms is sent to find Arion but her body is taken over by one of the shadows of the Anti-Monitor. Another Harbinger summons Psycho-Pirate from Earth-2.
The possessed Harbinger finds Arion from Earth-1's distant past and after toying with him she summons him as well. Meanwhile Another Harbinger summons Firestorm and Killer Frost from Earth-1. Harbinger gets Psycho-Pirate to make Killer Frost fall in love with Firestorm. The Monitor watches all of this. One by one superheroes and villains are called to the Monitor satellite. Others include the Golden Age Superman of Earth-2, Obsidian of Earth-2, Cyborg, Geo-Force, Green Lantern John Stewart, Dr. Polaris and Psimon all from Earth-1.
While on the satellite the confused group are attacked by Anti-Monitor Shadows. After a battle, the Monitor shows up and helps them defeat the shadows.