On August 12, 2011, a series of mysterious meteors crash into the ocean, wreaking havoc near 20 major coastal cities. What seems to be a natural phenomenon quickly reveals itself as a hostile alien invasion. With San Diego and San Francisco lost to the extraterrestrial forces, the remaining military stronghold is in Los Angeles (LA).
As LA braces for evacuation, Staff Sergeant Michael Nantz (Aaron Eckhart), a seasoned fighter and Iraq War veteran, is called in with Marines from Camp Pendleton. Although he is on the brink of retirement, Nantz is thrust into the chaos as he leads 1st Platoon, Echo Company, of the 2nd Battalion, 5th Marines. His presence is met with skepticism from his platoon, haunted by the fallout of his last mission in Iraq, where he lost many good men.
Under the guidance of the inexperienced 2nd Lieutenant William Martinez (Ramon Rodriguez), the platoon reaches a forward operating base (FOB) at Santa Monica Airport, ready to reclaim the city. With the Air Force preparing to bomb the area in a display of force, the platoon receives urgent orders to rescue civilians trapped at a local LAPD station. Battling their way through the alien-infested streets, the team suffers heavy losses during an ambush until Nantz’s quick thinking allows them to escape to safety.
Nantz, alongside Corporal Lee "Cowboy" Imlay (Will Rothhaar) and Corporal Kevin J. "Specks" Harris (Ne-Yo), embarks on a mission to locate the missing Private First Class Shaun "Casper" Lenihan (Noel Fisher). Their efforts lead to a chaotic encounter, where they manage to save Lenihan, who bravely battles an alien.
As they regroup with Technical Sergeant Elena Santos (Michelle Rodriguez), their efforts turn toward rescuing five civilians: veterinarian Michele (Bridget Moynahan), along with children Kirsten (Joey King), Amy (Jadin Gould), Hector (Bryce Cass), and Hector's father Joe (Michael Peña). In a pivotal moment, the Marines attempt to rescue their comrades but face brutal losses, illustrating the dire stakes of their situation.
Determined to fight back, the team commandeers a bus for their evacuation but quickly realizes how the aliens are leveraging their technology against them. Through their harrowing journey, they discover that the alien drones are locating targets via radio signals, which propels them to take calculated risks to outsmart their foes.
In the face of adversity, Lieutenant Martinez sacrifices himself to save his men, leaving Nantz in command. Together, they honor their fallen comrades and push forward to find a means of escape. With the radio signals still drawing the attention of their alien adversaries, Nantz devises a brave plan to confront the enemy, leading his team to a clandestine alien command center.
After fierce combat, the team manages to send a missile strike toward the enemy ship, resulting in a decisive victory as the alien drones fall from the sky. With death and destruction all around, the surviving Marines, including Nantz, Imlay, and Santos, are hailed as heroes upon their recovery from the battlefield. Though they are urged to rest, they refuse to sit idly by and opt instead to join the campaign to reclaim Los Angeles. Their story of courage becomes a beacon of hope against the encroaching darkness.
