After the deactivation of Megatron and the catastrophic time traveling events on Cybertron, the Autobots have made serious progress against the Decepticons. However a Cobra attack against G.I. Joe's base on Earth alters the balance of the war by unleashing Serpent O.R., an artificial super-soldier who proves to be nigh-unstoppable, and is imbued not only with the knowledge of past Earthen leaders, but the personality of Megatron himself! He soon travels to Cybertron and re-unites the scattered Decepticons into a force to be reckoned with once more.