Years ago, the noble dynasty of the Primes was betrayed by one of its own. A lone dissenter craved control over the Earth's sun, the ultimate source of energy, and so the others sacrificed themselves to keep the planet safe. Since then, more Transformers have arrived on Earth: the Autobots and Decepticons, who are sworn enemies. Now planet Earth is in danger again, and it's up to one robot to keep it from harm: Optimus, the last of the Primes.