En route to visit his girlfriend, Metamorpho, the Element Man, is compelled to skywrite an invitation to join the Justice League of America. An arrow appears to guide Metamorpho to the Secret Sanctuary. The Element Man is attacked by the Unimaginable, an alien being bent on taking Matamorpho's place in the Justice League of America. The Justice League of America aid Metamorpho in repelling the Unimaginable. Back at the Secret Sanctuary, Metamorpho declines the invitation to join the Justice League of America. Metamorpho reveals his origin, to explain his reasons for not wanting to be a super-hero.
The Batman tries to get the Justice League of America to focus on the threat of the Unimaginable. Metamorpho asks the Green Lantern to restore his lost humanity. The Green Lantern's power ring energy falls short of Metamorpho, revealing the Unimaginable. The Unimaginable has long been observing the adventures of the Justice League of America. Eavesdropping on their desire to add a new member to their ranks, the Unimaginable set out to prove it's superiority over Metamorpho. The Justice League of America decline the Unimaginable's offer to join their ranks.
In retaliation, the Unimaginable conjures forth alien threats, to imperil each individual member. By overwhelming the Justice League of America, the Unimaginable means to force it's way onto the team. By working together, the Justice League of America overcomes the Unimaginable's minions. Upon defeating his foe, Metamorpho carries the creature to the Secret Sanctuary, then covertly takes it's place. The Unimaginable gathers it's fallen forces, including the disguised Metamorpho, and returns to it's home world.
Metamorpho leaves a trail of his own atoms, for the Justice League of America to follow. Discovering the unconscious creature in their Secret Sanctuary, the Justice League of America realize what Metamorpho has done. Superman follows Metamorpho's trail of atom to the Unimaginable's home world. En route, the Justice League of America pass a sun going super nova. Realizing the Unimaginable powers itself from the radiation of the super nova, the Green Lantern transforms the team into energy waves, so that they, too are absorbed by the Unimaginable.
From within the Unimaginable's very body, the Justice League of America begin attacking the alien creature. Having utterly defeated the Unimaginable, the Green Lantern restores the Justice League of America to normal. The Justice League of America return to the Secret Sanctuary, along with Metamorpho, the Element Man. Once again, the Green Lantern tries to restore Metamorpho's lost humanity. The power of the Orb of Ra proves more powerful than the Green Lantern's power ring. Metamorpho cannot be restored to normalcy. Though declining active membership in the Justice League of America, Metamorpho agrees to take a standby position with the team.