Years after the Great War, the Autobot prison ship Alchemor crashes on Earth near Crown City, sparking a mass Decepticon jailbreak. Meanwhile, on a rebuilt Cybertron, war veteran Bumblebee is now working as a street cop, mentoring Cadet Strongarm. Bumblebee is alerted to the danger on Earth by a vision of a ghostly Optimus Prime, who directs them to a nearby space bridge.