While coping with the loss of his older brother, Spike Witwicky and his girlfriend Carly discover the derelict Ark spacecraft, just as the Autobots and Decepticons inside are reactivated. As the Cybertronian civil war resumes on Earth and humanity is forced to reckon with alien invaders, Optimus Prime and his few remaining troops must band together to protect this new world and its people from the Decepticon threat.