High-school student Sam Witwicky buys his first car, who is actually the Autobot Bumblebee. Bumblebee defends Sam and his girlfriend Mikaela Banes from the Decepticon Barricade, before the other Autobots arrive on Earth. They are searching for the Allspark, and the war on Earth heats up as the Decepticons attack a United States military base in Qatar. Sam and Mikaela are taken by the top-secret agency Sector 7 to help stop the Decepticons, but when they learn the agency also intends to destroy the Autobots, they formulate their own plan to save the world.

A youth chooses manhood. The week Sam Witwicky starts college, the Decepticons make trouble in Shanghai. A presidential envoy believes it's because the Autobots are around; he wants them gone. He's wrong: the Decepticons need access to Sam's mind to see some glyphs imprinted there that will lead them to a fragile object that, when inserted in an alien machine hidden in Egypt for centuries, will give them the power to blow out the sun. Sam, his girlfriend Mikaela Banes, and Sam's parents are in danger. Optimus Prime and Bumblebee are Sam's principal protectors. If one of them goes down, what becomes of Sam?

Autobots Bumblebee, Ratchet, Ironhide, Mirage (aka Dino), Wheeljack (aka Que) and Sideswipe led by Optimus Prime, are back in action taking on the evil Decepticons, who are eager to avenge their recent defeat. The Autobots and Decepticons become involved in a perilous space race between the United States and Russia to reach a hidden Cybertronian spacecraft on the moon and learn its secrets, and once again Sam Witwicky has to go to the aid of his robot friends. The new villain Shockwave is on the scene while the Autobots and Decepticons continue to battle it out on Earth.

For five years after the Decepticon invasion of Chicago, the Autobots were granted sanctuary into the Earth. Believing they are a threat, they were secretly eliminated by an elite CIA unit with the help of a Transformer bounty hunter, Lockdown. Because of this, Optimus has since lost his faith in humanity after the ambush that caused his injury and even considers leaving the planet until Cade Yeager, a mechanic, convinces him to reconsider his faith in humanity after helping him slightly recover. Together with his family, they join the Autobots to exterminate the bounty hunter, the reincarnated Megatron (in the form of Galvatron), and the Cemetery Wind (elite CIA unit tasked with killing Transformers).

Optimus Prime finds his dead home planet, Cybertron, in which he comes to find he was responsible for its destruction. He finds a way to bring Cybertron back to life, but in order to do so, Optimus needs to find an artifact that is on Earth.