Justice League vs. the Legion of Super-Heroes #4

The Justice League is trapped in the 31st century with the Legion of Super-Heroes, while the looming terror of the Great Darkness hovers over both time period simultaneously. Even as the great heroes of the 21st century get to experience the fantastic far-flung future, the mysteries behind the Gold Lantern and the Great Darkness threaten all of existence. What is the secret behind the Great Darkness? And will the greatest heroes of two ages be able to stop it before it's too late?