The Decepticons quickly try to build a space bridge before a prophesied darkness arrives.

Earth has an outbreak of natural disasters, caused by Dark Energon.

The Autobots acquire a surprising ally in their battle to save Earth.

The Autobots go to the Earth's core to fight for the planet; and Jack uncovers info about Optimus' background.

Megatron manipulates the impaired Optimus into joining the Decepticons.

Jack learns how to restore Optimus' memory.

Optimus begins to piece together his real identity using several clues (including Starscream referring to his as a "prime" -- whoops!), and eventually rebels against Megatron’s orders. Meanwhile, Optimus' Autobot pals hatch a risky plan to get their leader back.