Four years have passed since the Chicago tragedy and humanity continues to repair the damage, but both the Autobots and the Decepticons have disappeared from the face of the Earth. Now the United States Government is using the technology rescued from the Chicago siege to develop its own Transformers. Leading the project is Joshua Joyce ( Stanley Tucci ), an arrogant designer who thinks Autobots are technological junk and believes himself capable of making infinitely more advanced robots. Meanwhile, Cade Yeager ( Mark Wahlberg), an inventive mechanic, finds a Marmon semi-trailer. When trying to repair it, he discovers that the truck is not only a Transformer, but also Optimus Prime himself, leader of the Autobots. What Cade ignores are the consequences that may follow from this finding.