In the opening shots, there is a montage of news reports and politicians speeches about North Korea, interlaid with the opening credits and finally, the title of the movie itself appears on the screen.
Spokane, Washington. There is a high school football game where Matt Eckert's (Josh Peck) team loses because he gets cocky and keeps trying to run the ball in, even though he should be making more passes as the quarterback, like the coach tells him to.
After the game, he gets picked up by his girlfriend, Erica (Isabel Lucas), who's one of the cheerleaders in the school, and they go off to a party that night. At the party, the power suddenly goes out, but not knowing the circumstances of it, the teenagers continue to party, cheering loudly.
Back at the Eckert house, Tom (Brett Cullen) tells his returned son Jed (Chris Hemsworth) that he can't find the extra mattress, to which Jed replies that he could simply sleep on the couch. Matt arrives home and asks his dad whether he saw the game, to which he proudly replies that the team is lucky to have him regardless of the outcome. Tom is a police officer within Spokane and he needs to leave in order to investigate the power outage. Matt walks up the porch, sees Jed, and walks into the house without saying a word to him.
The next morning, Matt and Jed wake up to the rumbling sounds around them. Items around their house start to fall over, and they run outside to find out whats going on. They look up and see dozens of large aircraft with soldiers parachuting from them. One plane gets shot down by a ground-to-air missile and crashes into a nearby house.
The brothers get into their pickup truck and drive off to find their dad, who meets them along the way as he was driving towards them as well to regroup. They follow him towards the direction of the town outskirts as a descending paratrooper fires at them, but the Eckerts manage to run him over. Tom tells his sons to drive away to their cabin in the mountains for safety as he stays behind to help the rest of the townspeople. Reluctant at first, they soon comply and speed off.
We get our first detailed glimpses of the invading troops and realize they are North Koreans as they wear the symbol of the North Korean military. The Eckert brothers are pursued by other North Korean military vehicles that spot them as they try to save Erica before she is captured, but it is too late. Reversing direction, they manage to pick up a few more people, including schoolmates Robert (Josh Hutcherson) and Daryl (Connor Cruise), as some other escapees follow them in another car. They get to the cabin and try to compile as many supplies as they can. At night, they see a vehicle driving by, and Jed takes point with a rifle in case its a hostile. It turns out to be a non-military vehicle, but Pete (Steve Lenz) fires a wild shot at it with a handgun he found earlier, almost hitting Jed in the process. Jed orders him to hand the weapon over, but Pete refuses, so Jed takes it by force.
The following morning, they find out Pete left with all their food, so they gather what they can and leave the cabin. They scout around, but hear some sounds and see that a North Korean officer named Captain Cho (Will Yun Lee) is at their cabin with some soldiers and uses Tom and Daryl's fathers as bait to draw them out from the woods. Pete had betrayed them and gave away their location. Although Daryl's father is more compliant, Tom tells his sons through the megaphone to kill the bastard, pointing at Cho, and is shot by him as the soldiers burn down the cabin.
After a moment of mourning, Jed gives a speech about how this is their home, and the group decides to sow chaos among the invaders with guerrilla tactics, and learn how to operate the various weapons they could gather.
On their first raid, Toni (Adrianne Palicki) is sent as bait. She approaches a checkpoint and suddenly turns to run away, prompting several soldiers to chase her around a corner where she immediately ducks as the rest of the group rise from their cover and shoot down the soldiers. They then strip all their weapons and gear to take with them back to their new makeshift base in the woods.
Over the course of the next few days, they cause more chaos among the invaders by using stolen C4 and other explosives to blow up various military checkpoints, and outright shooting down other ground soldiers from rooftops with their captured small arms. They exclaim themselves to be the Wolverines, based on their school mascot, and the word spreads, causing others to rise up against their invaders.
At one outdoor public gathering where North Korean officials are speaking to the remaining people of the town, along with collaborators (Americans who have chosen to work with the invaders to spare their own lives) and a few allied Chinese and Russian military personnel, the Wolverines are preparing to take them out with live fire and explosives. However, Matt sees Erica, who is a prisoner at this point, being transported away in a school bus and sets off the explosions early. He is able to free her, and they escape within the chaos, but one of the other Wolverines is gunned down.
Jed is angry at Matt for disobeying and risking all their lives. Matt runs off, but after a few days, Jed goes to have a brotherly talk with Matt, where Matt accuses Jed of disappearing for six years when their mother died, leaving him and his father who too out his frustration by physically beating Matt. Jed admits he was wrong to do so since he was emotionally lost and needed to find himself, but that he needs him now, and they eventually reconcile and return to the group.
Meanwhile in Spokane, a high-ranking North Korean military officer barges into Cho's office, furious at him for being unable to stop the Wolverines, but Cho says he has a plan.
As the Wolverines rest up in their hideout, their shelter is suddenly destroyed when enemy jets bomb a large area of the woods. Two more are killed, and they go on the run. Only Matt, Jed, Toni, Erica, Robert, and Daryl are left. In the woods, they meet three American military personnel, led by Tanner (Jeffrey Dean Morgan), who coincidentally have been looking for the Wolverines.
Over a campfire, they realize that both groups had independently come up with the conclusion that the briefcase that Cho always carries with him is crucial to the invaders and must be captured. They go ahead with a raid on the local police station which the enemy personnel within the district have utilized as their base and manage to take down many of the soldiers. As Daryl is running away, he is caught and stabbed by some enemy Russian associates, but manages to escape. Meanwhile, Jed fights Cho, and they eventually end up in his fathers office inside the station. Cho gets the upper hand as Jed ducks under his father's desk, but he pulls out a gun from a hidden compartment to shoot Cho in the legs, causing him to collapse. Jed then finishes off Cho. Matt manages to retrieve the dropped briefcase from a fallen soldier, and he rejoins Jed to make a run for it.
They get away and hide out in a broken down house somewhere for shelter. Jed is proud of Matt, stating that he was never good at giving props to his brother, but that he deserved it this time. He gives his brother a beer, to which Matt replies it would be his first one, and they laugh. Jed then gets up to walk over to Toni, who is smiling at him in the hallway with another beer in hand, when he is suddenly shot and killed. The invaders had found their location and begin firing upon them. Matt yells for everyone to get out, and they manage to do so, getting into a car and speeding off.
They stop briefly in the woods to rethink their situation, and figure out that the enemy soldiers were able to find them because of a tracking device that has been embedded in Daryl's side. During the earlier battle, the Russians had actually embedded a tracker into him and allowed him to escape so that he would lead them straight to the rest of the group. Knowing it can't be removed, Daryl decides to stay behind with only a rifle as the others drive off.
The next scene shows other American military personnel and the four remaining Wolverines in a field as they load the briefcase onto a helicopter and prepare to take off. Tanner offers the surviving Wolverines the chance to go with them, away from the battle zone, but Matt refuses. The Wolverines decide to stay.
The final scene shows Matt atop a car, giving the same speech his brother gave to them near the beginning to more individuals wanting to fight against the invaders. That night, they storm the detention center where the invaders are keeping prisoners. The Wolverines attack with heavily armed jeeps and vehicles as people start shouting the name, and the last shot shows many of the resistance running forward with an American flag fluttering in the wind among them.