In the storyline, Hal Jordan, a member of the intergalactic police force known as the Green Lantern Corps, goes mad with grief after the destruction of his home town of Coast City during the "Reign of the Supermen!"

In a confrontation with the Justice Society of America, Extant ages several of them — removing the effect that has kept them young from the 1940s into the present day — leaving them either feeble or dead.

Calling himself Parallax, Jordan has gone insane and is now trying to remake the universe, undoing the events which have caused his breakdown and his own murderous actions following it.

DC published a fold-out timeline inside the back cover of Zero Hour #0 which identified various events and key stories and when they occurred.

Each ongoing series at the time retold the origin of its heroes in a #0 issue published after the end of Zero Hour and resumed their previous numbering the following month or went on to #1.

Following the end of Zero Hour, every DC Universe title published a #0 issue retelling the character or team's origins and featured the slogan "The Beginning of Tomorrow!"