A group of teenagers look to save their town from an invasion of North Korean soldiers.

An introductory montage shows the United States and its NATO allies weakened by the fallout of the economic crisis, an emerging alliance between an increasingly militant North Korea and ultranationalist-controlled Russia, and increased deployment of US troops abroad (and the highlighted threat of cyberwarfare) leaving the mainland vulnerable.

US Marine Jed Eckert (Hemsworth) is home on leave in Spokane, Washington. He reunites with his father, Spokane Police Sergeant Tom Eckert (Cullen) and his brother, football player Matt Eckert (Peck). The morning after a mysterious power outage, Jed and Matt are shocked to see swarms of invading North Korean paratroopers and transport aircraft. Their father tells them to flee to their cabin in the woods while he helps the townspeople. They are later joined there by Robert Kitner (Hutcherson), Daryl Jenkins (Cruise), and Pete (Lenz). Tensions build as the teens try to decide whether to surrender to the invaders or resist, with Pete in the end betraying their position. North Korean soldiers, under the command of Captain Cho (Lee), bring Sergeant Eckert and the mayor out to convince the group to surrender (with Cho shooting Eckert after he refuses to cooperate and actively encourages them to resist).

Afterwards, Jed announces that he intends to fight and the others agree to join him, calling themselves the Wolverines after their school mascot. After acquiring weapons, establishing a base in an abandoned mine, and being trained by Jed, the Wolverines begin a series of guerrilla attacks against soldiers and collaborators. The North Koreans respond by bombarding the surrounding woods to destroy the Wolverines' base. The Wolverines eventually encounter Marine Sergeant Major Andrew Tanner (Morgan) and two other Marines, Smith (Choi) and Hodges (Gerald). They reveal that the Russian-backed North Koreans launched an electromagnetic pulse (EMP) weapon that crippled the US electrical grid and military, followed by landings along the East and West Coasts (American counterattacks halted their advances and leave an area stretching from Michigan to Montana and Alabama to Arizona as "Free America"). They reveal that Captain Cho carries a suitcase containing an EMP-resistant radio telephone that would enable the US command to contact its remaining forces for a counter-offensive. The Wolverines assist Tanner, Smith, and Hodges in infiltrating the local police station, the North Koreans' center of operations, and succeed in stealing the suitcase (with Jed avenging his father's death by killing Cho). Hodges is killed in the gunfight.

After they successfully escape with the suitcase, the Wolverines regroup at their base. After a short conversation between Matt and Jed, however, the Wolverines are attacked and Jed is killed in the firefight. Visibly shaken, Matt and the rest of the Wolverines escape with the suitcase. The next day, Robert comes to the realization that during an earlier escape, Daryl had been tagged with a GPS tracking unit and has been being tracked since. After some thought, Daryl accepts the fact that they can't go on with him, so he stays behind, his fate unknown.

Sergeant-Major Tanner and Smith depart in a UH-1 with the suitcase, while the remaining Wolverines decide to stay behind and continue to fight, recruiting more members and raiding prisoner camps, with Matt now leading the effort.