Air strike scene on Scorponok Decepticons

Thousands of years ago, the planet Cybertron was consumed by a civil war between the two Transformer factions, the Autobots led by Optimus Prime and the Decepticons led by Megatron. The Autobots want to find the All Spark, the source of all Cybertronian life, so they can use it to rebuild Cybertron and end the war between the Autobots and the Decepticons, while the Decepticons want to use it to defeat the Autobots and conquer the universe. Megatron found the All Spark on Earth, but crash-landed in the Arctic Circle and was frozen in the ice. Captain Archibald Witwicky and his crew of explorers stumbled upon Megatron's body in 1897. Captain Witwicky accidentally activated Megatron's navigational system and his eye glasses were imprinted with the coordinates of the All Spark's location. Sector 7, a secret United States government organization, discovered the All Spark in the Colorado river and built the Hoover Dam around it to mask its energy emissions. The still-frozen Megatron was moved into this facility and was reverse engineered to advance human technology.
In the present, the rest of the Decepticons-Blackout, Scorponok, Frenzy, Barricade, Starscream, Devastator and Bonecrusher-have landed on Earth and assumed the disguise of Earth vehicles. Blackout and Scorponok attack the U.S. SOCCENT FWD military base in Qatar and try to hack into the U.S. military network to find the location of Megatron and the All Spark. Their mission is thwarted when the base staff severs the network cable connections. While Blackout destroys the rest of the base, Scorponok chases a small group of survivors who have photographic evidence of the robots, but he is eventually repelled. During this battle, the military discovers its only effective weapons against the Transformers' armor are high-heat sabot rounds.
After Blackout's failure, Frenzy infiltrates Air Force One to try again to hack into the military network, and in doing so plants a virus. He finds the map imprinted on Captain Witwicky's glasses, whose descendant, Sam Witwicky, intends to sell on eBay. Frenzy and Barricade begin tracking Sam's location. The Autonomous Robotic Organism (shortened to "Autobot") Bumblebee is also on Earth, disguised as a 1976 Chevrolet Camaro,[6] and is bought by Sam while shopping for his first car. Bumblebee helps him woo his crush, Mikaela Banes. Bumblebee leaves at night to transmit a homing signal to the rest of the Autobots and Sam sees him in robot mode. Barricade confronts Sam and demands Archibald's spectacles, but Bumblebee rescues him and Mikaela. After Bumblebee upgrades his vehicle form by scanning a 2006 Chevrolet Camaro, they leave to rendezvous with the rest of the Autobots: Optimus Prime, Jazz, Ironhide, and Ratchet-who have landed on Earth and taken the forms of Earth vehicles as well. Sam, Mikaela, and the Autobots return to Sam's home and obtain the glasses. Agents from Sector 7 arrive and capture Sam, Mikaela and Bumblebee.
Frenzy, disguised as a cellphone, secretly accompanies the group to Hoover Dam and releases Megatron from his frozen state. Locating the All Spark, Frenzy sends an alert to the other Decepticons. Sam convinces the Sector 7 agents to release Bumblebee so that he can get the All Spark to Optimus Prime. Frenzy's virus has shut down government communications, but a pair of hackers manage to establish a signal to the Air Force. The Autobot-human convoy goes to nearby Mission City to obtain a radio that will guide the Air Force's defense and secure a rendezvous point as a safe destination for All Spark. The Decepticons attack and Bonecrusher, Frenzy, Jazz, Devastator and Blackout are all killed during the ensuing battle, but Sam manages to ram the All Spark into Megatron's chest, killing Megatron and destroying the All Spark. Optimus takes a fragment of the All Spark from Megatron's corpse, but realizes that with its destruction, their home world Cybertron cannot be restored. Consequently, Optimus sends a signal to other surviving Autobots in the universe, directing them to their new home, Earth. The government orders the closure of Sector 7 and has the four Decepticons killed in Mission City battle dumped into the Laurentian Abyss. Starscream, who fled the battle, escapes into space.