The movie picks up not long after the battle in Chicago, about four years. Shia is out and Mark Wahlberg is in; he is a single dad and a failed inventor. Based on the way he interacts with his inventions, talking to them and hoping to coax them into working, instead of inspecting the wiring, circuit boards and software, its no wonder he's a failure. In fact, the whole personality he is assigned is rather dim --- he has a daughter he forbade from ever dating but seems to miss the fact she is super model hot. There is no reality where she is not dating, especially when you see the crowd she hangs with, all standard Bay-hotties. Meanwhile, Wahlberg has purchased a disabled Optimus Prime and nurses the guy back to health, just before he is betrayed by a co-worker and the government.
The next two and a half hours are running away, new autobots, dead autobots, explosions, a new comedic old guy character (Stanley Tucci who is a whole lot of fun), new style baddie robots (made by humans), the return of Megatron (duh) and another alien robot menace, again. Its, as they say, non-stop bay-splosions, car chases, battle scenes and deaths. We know there must be deaths but we only ever actually see one very visibly, the betraying co-worker. We knew he had to die but at least they make it count, kinda. Its all silly and over the top with tons of gramma screaming at the screen stupidities but, with a flick of the brain-switch, kinda fun. And there is Optimus Prime riding a fire breathing dinosaur robot while wielding a sword.