Plot

Sam Witwicky leaves the Autobots behind for a normal life. But when his mind is filled with cryptic symbols, the Decepticons target him and he is dragged back into the Transformers' war.

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?—<jhailey@hotmail.com>

As the humans of planet Earth are adapting to their new lives with the aliens, an old enemy returns from the dead to begin another war and get revenge on everyone. This time, the enemy has new allies to help battle against those who oppose him.—RECB3

In the year 17,000 B.C., the original Transformers leaders, the Seven Primes, travel across the universe to create Energon with star-absorbing machines called Sun Harvesters, which destroy stars in order to collect their raw material. One of them defies the rule to never destroy a planet with life on it by establishing a Sun Harvester on Earth, earning him the name "The Fallen". The Fallen is confronted by the other Primes, who imprison him before he can harvest the Sun using the Matrix of Leadership. The rest of the Primes then sacrifice themselves to hide the Matrix in an unknown location.

In the present day, two years after the Battle of Mission City, the Autobots and the U.S. military have formed the Non-biological Extraterrestrial Species Treaty (NEST), a classified international task force in order to eliminate the remaining Decepticons. In Shanghai, the Autobots intercept two Decepticons, Demolishor and Sideways. Sideways is killed by the Autobot Sideswipe, while Optimus Prime kills Demolishor, but not before he warns them of the Fallen's return. At NEST's secure headquarters in Diego Garcia, National Security Adviser, Theodore Galloway (John Benjamin Hickey), concludes that since Megatron's corpse is at the bottom of the Laurentian Abyss and the last known AllSpark shard is secure in their base, the Decepticons must still be on Earth solely to hunt the Autobots. The Decepticon Soundwave hacks into a military satellite, overhears this information, and sends Ravage and Reedman to retrieve the shard.

Meanwhile, Sam Witwicky (Shia LaBeouf) is preparing to attend college, leaving his girlfriend Mikaela Banes (Megan Fox) and guardian Bumblebee behind. He finds a smaller AllSpark shard in his hoodie and picks it up, causing him to see Cybertronian symbols. As a side effect, the shard's energy brings various kitchen appliances to life, who then attack Sam and his parents. After Bumblebee kills the living appliances, Sam gives the shard to Mikaela, who later captures the Decepticon Wheelie as he attempts to steal it. At the Laurentian Abyss, the Constructicons resurrect Megatron using the stolen shard and parts ripped off from one of their own allies. Megatron then travels to one of Saturn's moons, where he reunites with his second in command, Starscream, and his master, the Fallen, who orders him to capture Sam alive and kill Optimus, as Primes are the only Transformers who can defeat the Fallen.

In college, Sam is followed and seduced by Alice (Isabel Lucas), a Decepticon Pretender disguised as a college student, along with Mikaela and his roommate Leo (Ramon Rodriguez). Mikaela kills Alice, and the trio is captured by the Decepticon Grindor and taken to an abandoned factory. There, Megatron reveals that the symbols in Sam's mind will lead the Decepticons to a new Energon source, before Optimus and Bumblebee arrive to rescue them. Optimus engages Megatron, Starscream, and Grindor, killing the last in the process, before being himself killed by Megatron. The other Autobots arrive and force Megatron and Starscream to retreat. The Decepticons then launch devastating, simultaneous attacks around the world, while The Fallen hijacks Earth's telecommunications systems, demanding that Sam be handed over to him.

While looking for alien expert "Robo-Warrior", Sam, Mikaela, and Leo find and enlist the help of former Sector Seven agent, Seymour Simmons (John Turturro), who reveals the Transformers visited Earth eons ago and the most ancient, known as Seekers, remained hidden on Earth. With help from Wheelie, they track down a senile Decepticon Seeker named Jetfire at the Smithsonian Air and Space Museum. They use their shard to revive Jetfire, who Teleports the group to Egypt and explains the story of the Fallen. Along with Jetfire, Wheelie sides with the Autobots, and Jetfire sends them to locate the Matrix of Leadership, which could be used to revive Optimus. The group find the Matrix in Petra, but it disintegrates into dust. Nevertheless, Sam stuffs its remains into one of his socks.

Meanwhile, NEST forces and the Autobots land near the Giza pyramid complex and are attacked by a large force of Decepticons. During the battle, the Constructicons combine to form Devastator, who destroys one of the pyramids to reveal the Sun Harvester hidden inside, before he is killed by a U.S. Navy rail-gun aboard the USS Kidd. Ravage and the Decepticon Rampage attempt to spring a trap, using Sam's captured parents as bait, in order to force Sam to give them the Matrix, but Bumblebee interferes and kills them both. Major William Lennox and Sergeant Robert Epps (Tyrese Gibson) call in an airstrike that kills the majority of the Decepticon ground forces.

However, Megatron manages to shoot Sam, mortally wounding him. He then retreats after coming under attack by fighter jets. As Sam nears death, the Primes speak to him through a vision, saying that the Matrix must be earned, not found, and that he has now earned the right to bear it for fighting for Optimus. They restore Sam's energy and grant him the Matrix, which he uses to revive Optimus.

The Fallen Teleports to their location and steals the Matrix from Optimus. He returns to the pyramid with Megatron and activates the Sun Harvester. Jetfire, who is severely wounded after his battle with Scorponok, sacrifices himself to allow his parts to be transplanted to Optimus. The parts give Optimus immense strength and the ability to fly, allowing him to destroy the Harvester. He then battles Megatron and The Fallen, incapacitating the former and killing the latter. Megatron retreats with Starscream, vowing vengeance. The Autobots and their allies then return to the United States, and Leo and Sam return to college.