In the midst of global reports of meteor showers, Earth faces an unprecedented threat when it becomes clear that the meteors are actually a cover for an alien invasion. Marine Staff Sergeant Michael Nantz, who was on the verge of retirement after a fraught career, is assigned to lead a new platoon. As the world reels from the onslaught, the city of Los Angeles becomes a last stand for humanity. Nantz must now marshal his inexperienced troops to prepare for the urban combat that lies ahead, shaking off his past to confront the future.

The platoon is ordered to retrieve civilians from a police station in West Los Angeles before the U.S. Air Force bombs the area in a countermeasure against the alien forces. Nantz and his squad navigate the war-torn streets, integrating with other military units along the way. As they race against time to complete their rescue mission, the Marines encounter an enemy that is unlike any they have faced before: unpredictable, highly lethal, and technologically superior. The gritty reality of close-quarters combat puts the platoon's abilities to the test, and each member must rise to the challenge if there is to be any hope of saving the civilians, themselves, and what remains of their city.