When the Decepticons start experimenting on Cliffjumper's body with the fabled Dark Energon, the Autobots pick up the life signal of their lost comrade. They hurry to the site, where they find a huge Energon mine, under Decepticon control.
The Decepticons, in order to find the Autobot base, capture and torture Secret Agent Fowler, and it's up to Bulkhead and the three human kids to track him down. Meanwhile, Megatron raises an army of undead Transformers.
Through his Space Bridge, Megatron raises the dead Transformers of Cybertron, and summons them to Earth. The Autobots have to find a way to sabotage the Bridge, or else their new home will be destroyed by the legion of undead Decepticons.