The Justice League of America assemble at the Secret Sanctuary, responding to the emergency summons of five of it's members. Those five members arrive, via Green Lantern's power ring. Inexplicably, the Batman, the Green Lantern and the Flash have become giants. The Atom is one foot tall, as opposed to his usual six inches. The Green Lantern explains the situation. While in conflict with an alien dictator, on the planet Sstharssos, the Green Lantern suddenly grew to giant proportions. After defeating the dictator, the Green Lantern consulted his power ring, regarding the cause of his sudden increase in size.
The Green Lantern discovered that an antibody, picked up while he was inside the Unimaginable, was the root cause of his dilemma. The Green Lantern traveled to the Unimaginable's home world, to seek out a cure for his condition. Almost immediately, the Green Lantern had been attacked by an alien horror, one that had escaped the Unimaginable's imprisonment.The Green Lantern was saved by the timely appearance of the Batman and Superman. The Batman, too, had become a giant. Working together, Superman and the Green Lantern defeated the creature.
Back on Earth, police scientist, Barry Allen, and physicist, Ray Palmer, were struck with the same size increasing affliction. The Green Lantern drew Allen and Palmer to the Unimaginable's world, as the Flash and the Atom. While the five heroes discussed their dilemma, five more escapees, from the Unimaginable's confinement, descended on them. The Justice League of America found their increased size to be a disadvantage in the battle. Nonetheless, the team ultimately triumphed over their foes. Superman searched the planet for any trace of the Unimaginable, but could find none.
The Justice League of America was approached by another escapee, Doctor Bendorian. The alien scientist assured the Justice League of America that, given the right equipment, he could cure them of their affliction. Their situation, however, was more dire than they had imagined. Not only was their affliction contagious, transmittable by touch, but it would be fatal within ten hours. Thus, the Green Lantern teleported everyone back to the Secret Sanctuary, so that Bendorian could get to work. Super-powered crooks go on a crime spree, in a neighboring city.
The healthy members of the Justice League of America race off to confront the threat. Though the perpetrators looks like ordinary crooks, they quickly prove to possess phenomenal super=powers. After suffering a setback, the Justice League of America completely switch tactics, even swapping weapons, to overcome the crooks. Inexplicably, the Aurora Borealis begins moving down the coastline, menacing Gotham CityFr with powerful discharges of electricity. Bendorian gives his approval to the remaining members of the Justice League of America, to go out and face the threat.
After the Aurora Borealis has been dissipated, the Batman voices his suspicions about Bendorian, and asks the Flash to investigate them. Bendorian is revealed to be possessed by the Unimaginable. Once again trying to force it's way onto the team, the Unimaginable threatens to destroy the Earth. The Justice League of America refuse the Unimaginable's membership. The Unimaginable discovers that the Flash has sabotaged it's death ray. Superman punches Bendorian into unconsciousness. It is revealed that a simple period of total rest is all that is required to cure their affliction.