An ancient struggle re-erupts on Earth between two extraterrestrial clans, the heroic Autobots and the evil Decepticons, with a clue to the ultimate power held by a young teenager.

Decepticon forces return to Earth on a mission to take Sam Witwicky prisoner, after the young hero learns the truth about the ancient origins of the Transformers. Joining the mission to protect humankind is Optimus Prime, who forms an alliance with international armies for a second epic battle....