The opening scenes of the films replay the first moments of the invasion, showing news reports and live battle scenes of the actual battle including hazy aliens fighting humanity. The US army annouce that Los Angeles is the last stronghold on the east coast and that they will not lose the city no matter what.
Next the film skips to 24 hours before the first contact, Staff sergeant Michael Nantz wants to give up his career in the marines due to a action in Iraq in which he was the sole survivor out of a platoon of marines. He blames himself and just wants out to start and new life. But he still has to train the national guard and the marines.
During this other marines are enjoying themselves drinking and trying to lose one marine's virginity, with a bunch of girls but the man throws up and they leave for the night.
During the film, news and radio keep describing meteors suddenly emerging heading towards earth with some already close to hitting the east coast of America. News reports film the first meteors hitting tokyo and nothing is said or heard from them (probably US army trying to stop a panic). They begin to try to evacuate all civilians away from the coast line.
Mean while all marines and military personnel are called back from leave and staff sergeant Michael Nantz is placed in a rookie platoon with Lieutenant william Martinez to keep them together during the operations in the field. Which are thought to be simple evacuation orders of the population away from the coast line incase of a tsunami. Helicopters and armour is brought in which seems a little heavy handed with the use of live munitions being given out hundreds of rounds per each man.
The marines are given a briefing in which NASA state that the objects which are splashing into the ocean are slowing down before they hit the sea and are also mechanical in nature with a inner shell much like a drop pod. More and more meteors hit the ocean destroying several coast guard ships. News reports capture the first glimpses of the aliens as they rise out of the ocean and begin to fire into the crowds killing hundreds, news channels are in a state of shock. Exposions begin to erupt acrossed the city with other cities acrossed the globe reporting breaches by similar attackers.
Led by 2nd Lieutenant William Martinez the platoon boards a CH-46 Sea Knight and are transported to Santa Monica airport the new military FOB (forward operating base). Along the way Alien AA fire hits the helicopters but fails to bring down any of the aircraft. As they approach LA part of the entire down town area is in a pitch street to street battle with the alien hosts. But the Humans appear to be winning aircraft are seen strafing the aliens and tanks and artillery are pounding the alien infested zones to oblivion. No alien aircraft are spotted and the humans believe they claim the skies and deploy and firm defensive line to block the aggressive invaders from advancing passed towards the unevacuated areas.
A marine colonel who seems to be in command deploys several platoons including Martinez out to rescue the remaining civilians trapped inside the containment zone. As the military are ready to entirely fire bomb the whole of down town LA to stop the invaders once and for all before they can gather there forces. Given 3 hours they advance passing thousands of civilians fleeing the invasion, the platoon sets off heading towards a police station where people inside the hot zone had fled to escape the battle.
They then enter areas of the city where bodies line the streets and smoke fills the air stoping the marines from seeing much. Advancing they entire a housing neignbourhood where they are suddenly ambushed by a relatively small force of alien soldiers who ambush them firing from the roof tops with devastating fire power, several men are killed and rockets pound their cover. The marines shoot back but only one goes down, so they retreat into a apartment complex yard here the aliens cornor them and rush them. One alien attempts to grab a wounded soldier but is torn apart by bullets from the staff sergeant. As more marines are hit and seared by the alien weaponry, the sergeant finds and exit and drags the remains of the platoon back into a house where they defend themselves. Later they discover one soldier is missing and they go out to find him, killing a lone alien after it attacks in close combat. They leave it dead in a pool killed by a grenade after it falls in.
Advancing towards the station the platoon regroups with the remains of a second platoon who narrowly survived an ambush themselves, USAF Technical Sergeant Elena Santos is with them as was assigned to monitor the aliens communcations network before her squad got slaughtered. With extra help they approach the police station and find several survivors and call in a EVAC helicopter. The helicopter takes off with all the wounded marines as priority one wounded personnel, as it lifts it is struck but a alien drone aircraft and is destroyed with all personnel lost.
The battle is then turns into a utterly unwinnable battle where the aliens gain the upper hand with technology, speed, and numbers. The human air power is smashed out of the sky when hundreds of drones attack on mass, only the fighter jets such as F/A-18's and F-16's are able to stay in combat and can be seen firing missiles and depleted uranium rounds at alien aircraft, and all other helicopters and light aircraft are shot down, and the human armor strafed and destroyed. Hordes of alien forces begin to take over the streets and push back the marines and national guard deployed along the frontline, entire units are quickly destroyed.
With the aliens closing in 2nd Lieutenant William Martinez deploys his men to find transport to escape the area before the army nuke it, they hot wire a bus and escape the area after destroying a small alien patrol and torturing a wounded alien to find the most vulnerable part of their bodies. Along the way a drone attacks them lured by a radio signal, the staff sergeant cleverly straps it to a petrol station and blows the drone and the petrol station they discover the drones are unmanned.
They set off driving through the enemy forces and travel up onto the free way in which they finds is blocked, a single M1A1HA Abrams tank defends the route and holds the aliens off for a short amount of time so the marines can secure ropes to rope down 30 feet. The platoon slaughters the aliens before a support drone arrives and destroy the tank along with a humvee the marines manned, faced with the invaders over running them some sacrifice their lives so the civilans can escape down the rope. Martinez is mortally wounded by alien soldiers and sacrifices himself with all the platoon's c4 and finally destroys the entire group of aliens with the ground drone and the actual bridge allowing for the remaining 7 marines to escape back towards the FOB.
Later in the evening while caring for one of the wounded civilans they wait for the bombing just outside of the blast radius, but no bomb is dropped and the aliens begin to burn down the city razing it to the ground and stealing the planets water supplys. They drive to the destroyed remains of the FOB and find no survivors, stocking up on munitions and vehicles they drive to the nearest surviving EVAC running over squads of roaming aliens. They arrive and are the last out of the downtown LA.
The UH-1N Twin Huey helicopter takes them passed the alien buried central command drone, in which the staff sergeant believes he can take out, so the marines deploy using ropes and sneek passed the roaming alien guards into the sewage networks. Where they discover the alien command centre, they are discovered and quickly escape up a ladder and where they use a laser guided missile to destroy the command structures radar.
The aliens react faster then expected and lauched a counter attack with drones and infantry killing another marine, but take dozens of casualties. More missiles are fired but drones are used as shields for the command centre as it is pulled away. Finally one last missile is used which was almost destroyed by a drone but it destroys the command centre, All the drones in Los Angeles lose power and fall to earth blowing up on impact, with their air power lost the marines surge forward forcing the aliens to retreat.
Then the Staff sergeant and his team are evacuated by helicopter to a newly formed safe zone in the desert to the north of LA, where they ae greeted like heroes and they restock up on ammo and munitions, ready to go back to retake LA with the rest of the US forces. The marine colonel seen at the start of the film asks waht they are doing, Staff Sergeant Michael Nantz replies that he has to finish this. He leaves the tent and boards a helicopter with the rest of the regrouping US forces to retake Los Angeles.
Aaron Eckhart - SSgt. Michael Nantz
Michelle Rodriguez - TSgt. Elena Santos
Michael Peña - Joe Rincon
Ne-Yo - Cpl. Kevin Harris
Bridget Moynahan - Michele