The greatest heroes of two eras face their biggest threat...each other! Its the 21st century versus the 31st century, with all of reality at stake!One thousand years in the future, a Legion of Super-Heroes comes together to dedicate their lives to recapturing the great age of heroes of the 21st century. When the heroes discover that reality is falling to a great darkness in both times simultaneously, the Justice League and the Legion of Super-Heroes must team up to stop it all.Soon, the Justice League are trapped in the 31st century, and the looming terror of the Great Darkness hovers over both time periods 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?Two of DCs top super-teams clash, as threads from legendary writer Brian Michael Bendis runs on Legion of Super-Heroes and Justice League collide in a story with both the present and the future at risk!Collects Justice League vs. Legion of Super-Heroes #1-6.