After BumbleBee & the AutoBots Left CyberTron. Optimus gets Over-powered by the Decepticons. He is taken to their Leader, MegaTron. He refuses to tell wants to know where the AutoBots are going. He sends Shatter & DropKick, to find them. Before getting executed by MegaTron, Elita One (His Love), Ultra Magnus (his brother) & more AutoBots break-in & save Optimus. They take him to an AutoBot Hideout, and tell him that there is another way off CyberTron.
Flashbacks to Optimus' past, when he was named Orion Pax. Showing Optimus become a student for Alpha Trion. Showing his relationship with the 12 Primes, Elita (Ariel), Magnus, & his once great friend, MegaTron (who went by the name Megatronus, after the once Fallen Prime). Alpha Trion teaches Optimus the ways of a Prime, showing him a Primes' greatest virtues, Optimism & The Touch. Orion becomes Optimus Prime & gains the Matrix of Leadership (which is what present MegaTron wants). MegaTronous becomes Jealous, & showing his rise to become MegaTron, the leader of the Decpticons. Also at this time, he shoots Ariel, Optimus brings her to Alpha Trion & repairs her. But says she has a special power source keeping her alive, but also kills her if she uses it.
In present time, The AutoBots arrive to their destination. A battle ensues, Ultra Magnus leaves with the AutoBots. Optimus finds an escape pod, but Elita is lost, & sees what he thinks is Elita using her power.