This fic is about an android from the DCAU whose backstory won't make much sense unless you watch the Justice League episode "Tabula Rasa."
To keep it simple, Lex Luthor manipulates a power-copying android named AMAZO to fight the Justice League and, at the moment where Luthor and AMAZO are about to win, the android duplicates J'onn Jonzz's Martian telepathy and descovered Luthor's treachery.
After a brief skirmish that ended with AMAZO nearly killing Luthor, the android departs to the heavens to duplicate powers beyond those of Earth.