The story follows Alden Rockwell, a disgraced World War II veteran who is recruited for a dangerous mission after a series of brutal attacks occur on a remote Pacific island. The military believes the assaults were carried out by surviving enemy stragglers, but Alden is skeptical. Seeking redemption after a past failure that cost his squad their lives, he reluctantly agrees to join a small team of soldiers and scientists sent to investigate. Their arrival on the island is unsettling from the start, as they find abandoned camps, destroyed equipment, and signs of violent struggle without any clear explanation.

Tension grows as the team ventures deeper into the jungle, where they discover the remains of previous patrols and strange symbols carved into trees and rocks. The scientists begin to suspect the presence of a species or force unknown to military intelligence. At night, the team is stalked by unseen creatures that move with unnatural speed and precision. When the first attack occurs, it leaves the survivors shaken; the wounds on the bodies resemble something neither animal nor human. Alden senses that the mission briefing was incomplete and that the military knew far more about the island than they revealed.

As morale collapses, internal conflicts erupt between the soldiers desperate to escape and the scientists determined to uncover the truth. Alden attempts to maintain order, but his leadership is challenged by fear and dwindling resources. When they capture one of the assailants, they discover it is not an enemy soldier at all but a mutated being exhibiting vampiric traits. The creature’s existence confirms the scientists’ theory that a World War II-era medical experiment went horribly wrong, producing a contagion that transformed the island’s inhabitants decades earlier.

The remaining team members must now decide whether to flee or destroy the source of the mutation before it spreads beyond the island. Alden leads a final push toward an abandoned underground facility where the experiments originated. Inside, they uncover documents detailing the original project: an attempt to enhance endurance and strength in soldiers using biological manipulation. The project succeeded, but at the cost of creating uncontrollable predators driven by bloodlust.

In the final confrontation, Alden sacrifices the last remaining supplies of explosives to collapse the laboratory and seal the creatures underground. The survivors escape to the shoreline just as the facility detonates, engulfing the island in flames. A rescue ship pulls them aboard, but the military immediately confiscates their reports, hinting that the truth will remain hidden.

The film ends with Alden staring back at the burning island, aware that his redemption came at a high price—and uncertain whether the horrors he fought have truly been eradicated.