Since his return as Autobot leader, Optimus Prime has had visions of an ominous event. Amassing all their forces, the Decepticons stage a final attack that leads to the planet Nebulos, where the inhabitants find a way to merge with both factions as Headmasters. The ensuing battle sees newly built Autobots and Decepticons face off in an epic battle that will decide the fate of Earth and Cybertron.