Insurgents shoot down British fighter pilots Captain Kate Sinclair and WSO Terry Johnson over Afghanistan. After engaging in a fierce firefight on the ground, tragedy strikes when the insurgents kill Johnson, compelling Kate to flee to an old Russian bunker concealed underground. The relentless insurgents pursue her into a top-secret laboratory, where stray gunfire inadvertently releases terrifying creatures from their stasis chambers. In the chaos that ensues, Kate manages to escape back to the surface with the help of a friendly insurgent, Kabir Abdul Rahimi.
Upon being discovered by American soldiers, Kate and Kabir are taken back to their base camp where the commanding officer, Major Roy Finch, is skeptical of Kate's claims about the creatures. Nonetheless, he confiscates the microfilm she retrieved from the lab and makes a call to HQ. Kate then encounters a number of soldiers, including Sgt. Tom Hook, Corp. Kip Wilks, Corp. Jade Lafayette, Pvt. Dwayne Everett, Pvt. Eddie Serano, Pvt. Tucker O'Neill, and British soldiers Sgt. Oswald Jones, Trooper Dave Bromhead, and Trooper Vince Hughes.
As night falls, the creatures, having tracked Kate's whereabouts, descend upon the camp, plunging it into chaos. They wreak havoc, taking the lives of Serano, Everett, O'Neill, and Hughes in brutal confrontations. In the midst of this turmoil, Kate, Kabir, Hook, Finch, Wilks, Lafayette, Jones, and Bromhead seek refuge inside a shipping container, hoping to wait out the deadly attack.
When daylight emerges, Wilks inspects a carcass left by the creatures and determines that sunlight can harm them. Finch discloses alarming information from Army Intelligence: the creatures were birthed from a Russian operation that spliced alien DNA retrieved from a crashed spacecraft with human subjects, while the Afghan invasion served as a cover to secure these genetically engineered monstrosities for potential biological warfare.
The horror escalates when the carcass suddenly reanimates and assaults Kate with tentacles that temporarily take control of her mind. In a selfless act, Finch sacrifices himself by detonating a grenade to obliterate the attacking creature. Fueled by vengeance and survival, Kate, Kabir, Hook, Wilks, Lafayette, Jones, and Bromhead embark on a perilous mission to destroy the underground bunker. Wilks volunteers to stay outside, managing a Humvee's winch to facilitate the others' descent into the bunker through an elevator shaft.
Amidst the chaos, creatures capture Hook, prompting Kate to spearhead the rescue effort. The soldiers stumble upon the nightmarish truth of the Russian experiments—finding a massive creature contained in a tank as the intensity ramps up within the subterranean facility. The situation turns dire when a creature gruesomely bites off Lafayette's face and Jones heroically self-destructs, taking out a horde of monsters in the process. Amid the dreadful confrontation, Kabir recognizes one mutated being as his lost father just before the elevator crashes the Humvee down upon them. Outside, Wilks is occupied fending off insurgents.
In a thrilling escape, Kate and Hook return to the surface to rescue Wilks just in time, fleeing the area as a bomb is dropped on the bunker. The three surviving soldiers come to realize that a hidden conspiracy within the military still seeks to gain control over these ferocious creatures, setting the stage for further conflict.
