Last issue of JLA: Year One ended with the team distrusting the Martian Manhunter, whom they mistakenly thought was in control of some nefarious machine. Stumbling into the situation, it all goes wrong, and suddenly the sky is filled with fire:
J'onn attacks the machine, risking his life by being engulfed in flames, eventually destroying it. The sky of fire dies out, and along with it, the aliens. The JLA realize they've been wrong, but it may be too late: J'onn looks as though he is dying.
The JLA, enraged, follow the Locus soldiers via a teleportation beam back to their HQ. After a few minutes of a pitch battle, however, J'onn recovers and is able to help, but not before Locus' final stroke is enacted: a worldwide tectonic shift that will reconfigure Earth's landmasses and destroy all life!
The Flash, the all-but-official leader of the team, sends Green Lantern into space to try and stop the shift. While Aquaman, Black Canary, and J'onn continue to fight off the aliens, The Flash tries to reverse the program. He eventually does, while J'onn probes the aliens' minds, which trips a "fatal neuroshock", killing them all. It's...over?
A little while later, the team discusses what happened. They are still mad at J'onn for "spying" on them in their civilian lives, but come to realize it's mostly just because they really don't know one another, despite on depending on each other for their lives:
The rest of the team follows suit, but this detente is interrupted by a beaten and bruised Snapper Carr (unfortunately not dead), who tells the JLA that it is his Uncle Simon who is the missing, unknown alien. The Norad Alert goes off, and the JLA see now the scope of the plan: