When a few members of the Legion of Substitute Heroes commit a daring robbery, the Legion of Super-Heroes must face the possibility that the Subs have gone bad! However, it soon becomes evident that evil Legionnaires from the parallel universe of Earth-Three have invaded this universe, and they will stop at nothing to get what they want! Can the Legion defeat their ruthless counterparts, even with the help of the heroic counterparts of the Fatal Five? Introducing the Legion of Ultra-Villains and the Faultless Five!