NOTE: This spoiler was sent in by MingMachine.

Movie opens with brief explanation about the All-Spark, how it had the power to create life, and how the Autobots were searching for it.  But by the time they found out it was on Earth, it was too late...

Cut to Qatar, Middle East where Sgts Lennox (Josh Duhamel) and Epps (Tyrese Gibson) have just returned to base.  The base almost immediately comes under attack by Blackout, disguised as a MH53 Pave-Low helicopter.  He's basically unstoppable, and starts to hack the US defense network.  The base commander cuts the data cable with an ax, stopping the connection, but Blackout pretty much wipes out the base.  Lennox and Epps and a few other survivors escape with the only recorded image of the robot.  They are followed by the Scorponox, which detached itself from Blackout during the fight.

Now we meet Sam Witwicky, a girl crazy high school student trying to earn grades and money so his dad will fund his purchase of a car.  His great-grandfather was a famous Arctic explorer, we learn through Sam's class presentation, who went mad and died in a nuthouse.  Now Sam's trying to sell all of his antique explorer gear on Ebay.  Of particular interest are the great-grandfather's cracked glasses...

Sam makes the grade on his report, and eagerly goes with his dad to buy a car.  After a prank visit to a Porsche dealership, Sam's dad takes him to a rundown used car lot to buy the real car.  As the dealer (Bernie Mac) tries to sweet talk them to buy other junky cars, an old yellow camaro with black stripes mysteriously appears in the lot and basically forces Sam to buy it by blowing out the other car's windows.

Now with a relatively cool car, Sam goes off to impress the ladies, in particular Mikaela Banes (Megan Fox), who's currently with (what else?) a stupid jock.   He drives out to a lake where she and the jock are hanging out, and tries to fit in.  Sam makes some witty remarks when the jock insults him, and lucks out even more when the jock pisses Mikaela off with a sexist comment.  He offers her a ride home and even though he's a nervous dork, his car seems to play the most appropriate songs and conveniently "stalls" next to a romantic overlook.  Through the conversation with Mikaela we learn that she's car whiz trained by her mechanic dad.  Sam finally drops her off and is giddy about the "date" he just had.

That night, Sam is awakened by the sound of the car driving off, and chases after it, calling the cops along the way.  He tracks it to a junkyard, where he sees the transformed Bumblebee in robot form shining a signal light into space (think the Bat signal, but with the autobots logo)  Freaked out, he tries to run, but instead gets arrested by the cops, who think he's the car thief.  He's released after being grilled by a jerk detective.

Now we get the 3rd storyline in Washington as we meet Maggie Madsen (Rachel Taylor), a young signal processing genius recruited by the Secretary of Defense John Keller (Jon Voight) to analyze the decepticon signal recovered from the Qatar base.  At the same time, the tiny decepticon Frenzy has somehow snuck on board Airforce One and starts to hack the defense network again using the computer terminal on the plane.  This time, he finds what they were looking for, which turns out to be the name of Sam's great-grandfather, and plants a virus in the network to boot.  Maggie is the first one to detect the attack, and notices the signals are the same.  Meanwhile, Frenzy sneaks off Airforce One and hops into the waiting Barricade, disguised as a police cruiser. and the 2 go off in search of Sam.  Maggie forms a theory about the attackers being "DNA-based" computers, but no one listens.

As these stories are happening, Sgts Lennox and Epps stagger into a village, where they are attacked by the Scorponox.  After finally regaining contact with the pentagon, they are able to call in an airstrike to kill it.  They are rescued and on their way back to the US they examine the scorponox's remains, finding out that it was vulnerable to high heat rounds.

Sam's car drives off again by itself, and Sam chases it on bike.  He runs into Mikaela during the chase, and she tries to follow.  Barricade shows up and joins in the chase, cornering Sam and knocking him around, asking him about his Ebay auction.  Bumblebee shows up in time to rescue Sam and Mikaela, and Barricade chases them.  After a long car chase, Bumblebee and Barricade go mano-a-mano while Frenzy chases after Sam and Mikaela.  Mikaela decapitates Frenzy with a jigsaw and Bumblebee pounds Barricade.  Finally face to face, Bumblebee communicates with Sam and Mikaela through using various audio clips from songs and movies, and convinces them to drive off with him.  Before they leave, however, Frenzy's head is able to transform into Mikaela's phone and sneak off in her purse.  During the drive, Mikaela complains about Bumblebee's crappy looks, and Bumblebee scans and transforms into a brand new camaro.

Meanwhile, back in DC, Maggie sneaks out a copy of the decepticon signals and takes them to master hacker Glen Whitmann (Anthony Anderson), who recovers the phrases "Project Iceman" and "Sector 7" from the files before both are arrest by the Feds.

Four flaming pods crash into the earth at various spots, and "naked" autobots emerge.  Conveniently enough, each one of them is near a GMC vehicle for them to scan, and soon Ratchet (a Hummer tow truck), Ironhide (pick-up truck), Jazz (Pontiac Solstice), and Optimus Prime roll out to meet Sam.

Prime lays it out for us: The autobots' homeworld was destroyed in a civil war with the decepticons led by Megatron.  The All-Spark will give Megatron the power to control and transform all technology on earth, creating a new decepticon world and driving humans to extinction.  Megatron crashed into the arctic while searching for the spark, trapped and frozen until Sam's great-grandfather found him.  He's the "Project Iceman" from Maggie's file.  After accidentally activating Megatron's navigation system, the coordinates to the All-Spark was etched into the grandfather's glasses.  The same glasses Sam is selling on EBay.

Rushing home, Sam and Mikaela desperately search for the glasses while trying to hide the autobots from Sam's parents.  Just as Sam finds the glasses, men in black types from the mysterious Sector 7 show up and arrest everybody.  Prime and company rescue Sam and Mikaela, but are outnumbered.  After a bit of chasing, Sam and Mikaela are recaptured along with Bumblebee, who is frozen and dragged off by Sector 7.  We find out that Sector 7 has been aware of the existence of the autobots and are equipped to capture them. 

Back in DC, secretary Keller gets a visit from a Sector 7 creep just as worldwide communications is shut down by the decepticon virus planted by Frenzy.

Now everything starts to come together.  Prime and the gang get the coordinates from the glasses and set off to rescue Sam; Secretary Keller recruits Maggie and Glen as advisors; Sgts Lennox and Epps are whisked off by Sector 7 as soon as  they land back in the US; and everybody winds up on the same chopper as Sam and Mikaela heading to the same place: Hoover Dam.  Once there, we find out the whole dam is a cover for a Sector 7 base deep underground.  We also find the father of modern human technology: Megatron!  It seems that every technological invention since the 1800's has been reverse engineered from Megatron, who is still frozen in ice and held in a hanger.  Along with the big M himself, Sector 7 also has the All-Spark stashed in the same facility.  Sector 7 uses the dam to mask the energy signatures from the spark while they continue to study it.  As everyone is taking a tour of the facility, Frenzy's head sneaks out of Mikaela's purse.  He's completely rebuilt by touching the All-Spark, and sends out an SOS to all Decepticons.  We finally see the rest of the decepticons: Starscream (F-22 Raptor), Bonecrusher (Buffalo mine protected vehicle), and Devastator (big ol' tank) spring into action along with Barricade and Blackout.

Starcreams arrives first and takes out the power to the base, which starts thawing Megatron.  Sam convinces Sector 7 to free Bumblebee, who causes the All-Spark to collapse into a convenient, easy to carry cube.  The mission is to get the All-Spark as far away from Megatron as possible before he gets free.  Lennox and Epps lead a company of soldiers to escort Bumblebee, Sam and Mikaela to the nearest city while Keller, Maggie, and Glen try to get communications up so they can have air support.  Along the way, Sam runs into the autobots and they join the soldiers in the protection convoy.

Megatron finally emerges and tears his way out of the hanger, where he is joined by Starscream. Sam's convoy is attacked by Bonecrusher, and Optimus stays behind to fight him off.  He stabs Bonecrusher through the head as the rest of the group makes it to the city and try to set up defenses.

Maggie, Keller and Glen find an old radio which they try to hook up to a computer to send out morse code to the air force.  As Glen tries to hook everything up, Frenzy attacks.  Maggie and Keller keep Frenzy at bay while Glen finally gets the signal out to get air support for Sam's group.  Frenzy ends up decapitating himself with one of his throwing blades and is really dead this time.

Back at the city, everything seems ok until Starscream, disguised as a friendly fighter jet, attacks with missiles.  The autobots get in the way to deflect some of the damage, and Bumblebee loses his leg.  In the chaos that follows, the rest of the decepticons attack, forcing everyone to fall back. 

Megatron rips Jazz into pieces and tussles with Prime for a bit when he finally shows up.  Sam has to get the all-spark to the top of a building, where he'll be rescued by choppers.  Lennox and Epps hold off Devastator, while Ratchet and Ironhide try to protect Sam from the rest.  They're hurt pretty badly in the process, and Sam races to the top of the building with Megatron chasing.  Mikaela hotwires a tow truck and drives the injured Bumblebee to rescue Lennox and Epps.  Together, they shoot Devastator full of holes.

The choppers come in to pick up Sam, but are shot down by Starscream.  Megatron knocks Sam off the building, but he's rescued by Prime. Prime tells Sam that if he can't beat Megatron, Sam must insert the All-Spark into Prime's chest, which will overload and kill Prime and destroy the spark.  Megatron and Prime face off for the big fight.  As they go at it, Blackout tries to sneak up on Prime.  Lennox and Epps arrive in time to coordinate the arriving air support.  Even with Starscream ambushing them, the F-22 fighters blow Blackout away, and critically wound Megatron, who was gaining the upper hand on Prime.  Sam is caught between Megatron and Optimus, who are both crawling towards him.  Optimus asks Sam to put the spark into his chest, but instead Sam shoves it into Megatron's, overloading and killing him.  Prime and the surviving autobots and humans gather and mourn the loss of Jazz.  Bumblebee asks to stay with Sam.

In the end, the remains of the decepticons are dropped into the deepest sea trench, Sector 7 is disbanded, Lennox returns home to his wife, and Sam and Mikaela make out on top of Bumblebee's hood. Prime says the autobots will remain on earth to protect, and sends a call out to any surviving autobots in the galaxy.

In the credits, there's a quick shot of Starscream flying into space...

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After an epic battle moving from the Hoover Dam to a nearby city, resulting in the deaths of Bonecrusher (decapitated by Optimus Prime), Brawl/Devastator (taken down by Bumblebee and the military), Blackout (Taken down by Captain Lennox), Jazz (bisected by Megatron) and Frenzy (comically self decapitated), with Bumblebee incapacitated (legs blown off by Starscream's attack), Sam (Shia LaBeouf) takes the Allspark to the top of a building, where Megatron (voice of Hugo Weaving), seeking to use the Allspark to transform Earth into a technological world and rebuild his army follows him. Sam signals the military to take the Allspark from him but the military helicopter is attacked and destroyed by Starscream. Megatron then tries to attack Sam, sending him off the building to be just barely caught by Optimus Prime(voice of Peter Cullen). The three fall to the ground where Optimus charges Sam with the duty of pushing the Allspark into his spark, which would kill him but also destroy the Allspark. Optimus and Megatron engage in an all out battle to finish each other off (opening with the throwback "One shall stand, one shall fall") which ends in stalemate. Prime tells Sam to Put the Allspark into his chest, but Sam instead directs it at Megatron, and the surge of energy wipes out the allspark and kills Megatron. All of the decepticons are thrown by the military into the worlds deepest oceanic trench, so that they would stay in stasis lock forever. Bumblebee decides to stay with Sam, who ends up with Mikaela(Megan Fox). Captain Lennox(Josh Duhamel) returns home to his wife and baby daughter, and Ironhide, Ratchet and Optimus Prime stay with their human allies, and Optimus sends a message hoping to reach other surving Autobots.

After the credits start to roll, Starscream is seen escaping Earth's atmosphere. Barricade and Scorponok are not shown to die, leaving open the possibility for a sequel appearance.