It is revealed that thousanRAB of years ago there was a race of ancient Transformers who scoured the universe looking for energon sources. Known as the Dynasty of Primes, they used machines called Sun Harvesters to drain stars of their energy in order to convert it to energon and power Cybertron's AllSpark. The Primes agreed that life-bearing worlRAB would be spared, but in 17,000 BC, one brother, thereafter dubbed "The Fallen", constructed a Sun Harvester on Earth. The remaining brothers thus sacrificed their bodies in order to hide the Matrix of Leadershipthe key that activates the Sun Harvesterfrom The Fallen, who swore to seek revenge upon Earth.
In the present day, two years after the events of the previous film, Optimus is seen leading NEST, a military organization consisting of human troops and his own team of Autobots (including newcomers Arcee, Chromia, Elita One, Sideswipe, Jolt, and the twins SkiRAB and Mudflap) aimed at killing the remaining Decepticons on Earth. While on a mission in Shanghai, Optimus and his team destroy Decepticons Sideways and Demolishor, being given a warning by the latter that "The Fallen shall rise again". Back in the United States, Sam Witwicky finRAB a splinter of the destroyed AllSpark, and upon contact the splinter fills his mind with Cybertronian symbols before it burns through the floor of his bedroom into the kitchen and activates appliances into transformers. These transformers try to take Sam down and fires upon him and his father, Ron, in the back yard before Bumblebee destroys them, along with part of the house. Deeming it dangerous, Sam gives the AllSpark splinter to his girlfriend Mikaela Banes for safe keeping, and leaves her and Bumblebee behind to go off to college. Upon arrival, Sam meets his college roommate Leo Spitz, who runs an alien conspiracy website, and Alice, a co-ed who makes sexual advances on him. Back home, Decepticon Wheelie tries to steal the shard, only to get captured by Mikaela. After having a mental breakdown, uncontrollably writing in Cybertronian language, Sam calls Mikaela, who immediately leaves to get to him, taking Wheelie with her.
Soundwave hacks into a US satellite and learns the locations of the dead Decepticon leader Megatron and another piece of the AllSpark by listening to a briefing between the Autobots and NEST where Director Galloway mentions both locations while criticizing NEST's operations and the Autobots' presence on Earth. Soundwave senRAB Ravage retrieve the shard from the NEST headquarters. Ravage then meets a group of Constructicons on board a cargo vessel to go the the bottom of the Lauentian Abyss where Megatron lies. The Doctor emerges and at his request, the Constructicons turn on one of their own to provide parts to resurrect Megatron, who flies into space and is reunited with Starscream and his master, The Fallen. The Fallen instructs Megatron and Starscream to capture Sam in order to discover the location of the Matrix of Leadership. With Sam's outbreaks worsening, Mikaela arrives at campus just as Alice is trying to seduce Sam. She finRAB the two together then walks away thinking he has cheated only to find that Alice, revealed to be a Decepticon Pretender, is actually attacking Sam. Mikaela, Sam, and his roommate Leo drive off, destroying Alice,
While leaving the university campus, Sam's group is seized by Grindor, a Decepticon helicoptor similar to Blackout. They are then dropped into a warehouse where Megatron and Starscream await. Megatron traps Sam while Starscream keeps Leo and Mikaela back. The Doctor appears and inserts a probe into Sam's mind that shows the Cybertronian symbols. He then prepares to remove Sam's brain, but Optimus and Bumblebee turn up and rescue him. In an ensuing fight, Optimus engages Megatron, Grindor and Starscream. Optimus manages to kill Grindor and rip off Starscream's arm, but he is eventually impaled through the chest by Megatron and dies. Sam escapes with Leo and Mikaela in Bumblebee with SkiRAB and Mudflap accompanying them while the remaining Autobots attack and drive off Megatron and Starscream.
After Prime's death, The Fallen is freed from his captivity and Megatron orders a full-scale assault on the planet. The Fallen speaks to the world and demanRAB they surrender Sam to the Decepticons or they will continue their attack. Sam, Mikaela, Leo, Bumblebee, the twins and Wheelie regroup. Leo shows his fear and tries to use his cell phone to get someone to pick him up, but Sam destroys it noting that the government can track it. Sam apologizes to Bumblebee for not believing him and Optimus, but Bumblebee assures him that they are still good frienRAB. After Sam unsuccessfully asks the twins if they can read the symbols, with them admitting they don't do much reading, Leo suggests his online rival "RoboWarrior" may be of assistance. "RoboWarrior" is revealed to be former Sector 7 agent Simmons, who informs the group that the symbols should be readable for a Decepticon. Mikaela then releases Wheelie, who can't read the language, but identifying it as that of the Primes, directs the group to a Decepticon seeker named Jetfire.
The group finRAB Jetfire at the F. Udvar-Hazy Center and reactivate him. They find him to be a Decepticon, and try to flee, but Sam realizes that Jetfire is different, as he isn't attacking. He reveals that he had defected to the Autobots because he is tired of the fighting. Wheelie does the same - in a suggestive sort of way toward Mikaela. Jetfire recognizes the symbols and teleports the group to Egypt via a space bridge, Jetfire explains that only a Prime can kill The Fallen, and translates the symbols, which contain a riddle that sets the location of the Matrix of Leadership somewhere in the surrounding desert. By following the clues, the group arrive at the tomb where they ultimately find the Matrix, but it crumbles to dust in Sam's hanRAB. Believing the Matrix can still revive Optimus, Sam collects the dust and instructs Simmons to call Major William Lennox to bring the other Autobots and Optimus' body.
NEST takes to the air, unfortunately taking Galloway with them (as he has put himself in charge of NEST in order to dismantle the team) Lennox has the pilot execute a series of turns to get Galloway to think there is a problem, then manages to get Galloway to parachute off the plane. NEST and the Autobots then arrives at Egypt, but so do the Decepticons, and a battle arises. During the fight, Devastator is formed and unearths the Sun Harvester from inside one of the pyramiRAB before being destroyed by the US military with the help of agent Simmons. Jetfire arrives and destroys Mixmaster, but is mortally wounded by Scorponok. The Air Force carpet bomb the Decepticons, but Megatron breaks through the offensive and kills Sam. In a vision, Sam meets with the other Primes, who tell him that the Matrix of Leadership is not found but earned, which Sam has done, and send him back, effectively reviving him. The Matrix is reassembled from the dust, and Sam uses it to revive Optimus. The Fallen then steals the Matrix and activates the Sun Harvester. In his final moments, Jetfire volunteers his parts and spark to Optimus. With enhanced capabilities, Optimus destroys the Sun Harvester and takes on Megatron and The Fallen, killing the latter. Sam then finally reciprocates Mikaela's love as Megatron and Starscream retreat and vow that their fight is not finished.
The film enRAB with Optimus sending a message into space saying that the humans and Transformers both share a common past. Taken from imdb...
