THE DOMINATORS, a race of aliens that truly live up to their name, have rounded up dozens of Earthlings to conduct tests. They want to know what it is about our planet that produces such a wide variety of genetic mutations, and so they put the randomly selected humans (including the Justice League's old pal, Snapper Carr) through a series of very lethal tests. After six humans survive a test that only one could have statistically survived, the Dominators conclude that humanity's genetic potential is too great a risk to their plans of conquest.
To that end, they recruit other alien races to join them in an invasion of Earth. Their stated purpose: to remove all so-called "superheroes" from the planet, but what the Dominators don't tell their allies is that they plan to use the invasion as a cover for their own research into creating genetically superior soldiers.
Led by the Dominators and the warlike Khunds, the alien armada scores several victories at first, establishing a beachhead in Melbourne, Australia, invading several parts of the world (Cuba, Russia, the North Pole) and causing the deaths of several heroes.
While the heroes launch a counterattack, one lone Dominator reveals that he has discovered the secret of the "metagene," the genetic factor that can turn people into superhumans in certain situations. He uses his research to create a "gene bomb," which, when detonated, will destroy every human carrier of the metagene.
Meanwhile, in the alien prison known as the Starlag, the Dominators' prisoners -- a collection of the surviving human guinea pigs and other alien species -- start a revolt against their captors. The heroes then receive help from an unexpected source and succeed in driving back the invading force. But there's little time to celebrate before the gene bomb is detonated, leaving the heroes to deal with both the sick and dying heroes and a new crop of people suddenly bestowed with amazing new powers.