Justice League #21

Synopsis

Having traveled back in time even further, the Flash explains to Batman the problem, and the two leave the rest of the Justice League fighting an alien to try and figure out what goes wrong with the power source demonstration before it happens. They uncover a plot to sabotage the demonstration and the League regroups to try to stop the explosion, but all that was needed was rejoining the alien tech powering the energy source with its owner, the alien with whom the League had just fought.