Omelete has posted a new, more detailed description for the story and main human characters for Transformers: Age of Extinction. This has not been officially confirmed but does go along with previous synopsis, interview info and leaked information from the past few months so inclined to believe its accuracy. Below is a translation from TFW2005. Spoiler warning (just in case).
"Four years after the Battle of Chicago, the government is using reverse-engineered leftover technology to build their own Transformers. Joshua (Stanley Tucci) is an arrogant designer who believes the Autobots are "pieces of junk" and creating his own robots is a form of art. He's fills basically the same role as Agent Simmons from the previous trilogy.
Cade Yeager (Mark Wahlberg) is a widowed inventor who lives in a farm with his daughter Tessa (Nicola Peltz), unaware that she's dating a race car driver, Shane (Jack Reynor). Cade finds a piece of Cybertronian technology and takes it back to his farm, but it is accidentally activated, leading the government and alien bounty hunters to his farm. The bounty hunters (it's unclear if they're connected to the Decepticons) have antigravity weapons which they use to abduct Tessa. In another scene, an entire transatlantic cruise ship is raised out of the ocean and crosses through a busy intersection while the protagonists are in the middle of a car chase.
Sophia Myles is playing Darcy, Joshua's assistant and an archaeologist. Cade, Tessa, Shane, Joshua and Darcy are the main human character, and the main subplot is Shane trying to prove his worth to Cade. Also, Cade addresses Bumblebee as "Bee" and calms him down when Joshua trash-talks him, indicating he might be Bumblebee's new owner.
Titus Welliver's character, Savoy, is the leader of a team of agents sent by Harold Attinger (Kelsey Grammer) to capture the protagonists."