Optimus Prime and the Autobots investigate the return of the Decepticons while forced to account for a group of young humans who unwittingly become involved in their eons-old conflict.

When a weak life signal is received from Cliffjumper, the Autobots roll out and are met by newly-returned Megatron who has obtained a mysterious and powerful substance... Dark Energon!

Bulkhead is on a mission to rescue Agent Fowler, who has been kidnapped by the Decepticons. Complications arise when Miko secretly tags along.

Utilizing the Dark Energon, Megatron summons an army of undead warriors to battle Optimus, while the other Autobots launch a high-stakes rescue onboard the Decepticon warship.

The ultimate showdown unfolds in Earth's orbit as the Decepticons, aided by Megatron's undead army, do battle with the Autobots with the fate of the Earth hanging in the balance.