It is revealed that thousands of years ago there was a race of ancient Transformers who scoured the universe looking for energon sources. Known as the Dynasty of Primes, they used machines called Sun Harvesters to drain stars of their energy in order to convert it to energon and power Cybertron’s AllSpark. The Primes agreed that life-bearing worlds would be spared, but in 17,000 BC, one brother, thereafter dubbed “The Fallen”, constructed a Sun Harvester on Earth. The remaining brothers thus sacrificed their bodies in order to hide the Matrix of Leadership the key that activates the Sun Harvester from The Fallen, who swore to seek revenge upon Earth.
In the present day, two years after the events of the previous film, Optimus Prime is seen leading NEST, a military organization consisting of human troops and his own team of Autobots (including newcomers Arcee, Chromia, Elita One, Sideswipe, Jolt, and the twins Skids and Mudflap) aimed at killing the remaining Decepticons on Earth. While on a mission in Shanghai, Optimus and his team destroy Decepticons Sideways and Demolishor, being given a warning by the latter that “The Fallen will rise again”.
The battle for Earth has ended but the battle for the universe has just begun. After returning to Cybertron, Starscream assumes command of the Decepticons, and has decided to return to Earth with force. The Autobots believing that peace was possible finds out that Megatron’s dead body has been stolen from the US Military by Skorpinox and revives him using his own spark. Now Megatron is back seeking revenge and with Starscream and more Decepticon reinforcements on the way, the Autobots with reinforcements of their own, may have more to deal with then meets the eye.