Dr. Ash Mattley (Mark Dacascos), a doctor in a small village deep in the jungles of Borneo, is approached by another scientist, Dr. Carl Wessinger (Jürgen Prochnow) regarding his studies of an enzyme found in a rare beetle. With the aid of Mattley and a group of natives, Wessinger secures several of the beetles, but then betrays his team and leaves them behind in a cave. Later, Wessinger uncovers a fossil in the jungle, but the natives in his new team fall in fear and worship before the deceased creature, which they call Balacau.
Two years pass, and Mattley's clinic is beset by a series of gruesome murders in the jungle. The natives attribute the killings to Balacau, an ancient myth in the area come to life. Mattley is approached by Claire Sommers, a CIA agent (Robin McKee), who enlists his aid to find Wessinger. Wessinger had been working for the United States government but fell out of contact, and Sommers reveals she has been sent to track him down. Together with Matzu, (Tom Taus), a boy whose sister was one of the victims, they set out into the jungle. Mattley does not initially believe that Balacau is real, but Sommers eventually tells him that the CIA was funding Wessinger's research into the fossil, leading him to change his mind.
Mattley and Sommers eventually reach Wessinger's compound, only to find it abandoned. When they examine the computers in the main lab, they find that Wessinger used the enzyme from the beetles to reanimate Balacau's fossil; Wessinger's records reveal it was an alien creature that terrorized the jungle centuries earlier. He intended to make clones of it for sale to the highest bidder, but it grew hostile and escaped. Balacau returns to the compound and pursues Mattley and Sommers, who end up separated from Matzu but find Wessinger and his assistants in a panic room. The two groups team up to keep the compound's power on and find Matzu. Balacau attacks in the main lab, but the flashing of Sommers's camera and the light from an arriving helicopter frighten it away. A band of mercenaries led by Sergeant Reinhardt, Mark McCracken, that work for Wessinger arrive, ostensibly to aid in recapturing the creature, but instead help Wessinger subdue and imprison Mattley and Sommers. They also decide to use Wessinger's assistant, Azenfeld (Roger Aaron Brown) as bait for the creature, but Mattley and Sommers escape and free him. In the ensuing battle, Azenfeld sacrifices himself to set off a bomb that kills Wessinger, Reinhardt, and most of the mercenaries.
Mattley, Sommers and Matzu escape into the jungle, pursued by both the remaining mercenaries in a second helicopter and Balacau; the creature is able to track them using invisibility and infrared vision. After destroying the helicopter, they are attacked by Balacau, and Matzu is killed when he warns Mattley and Sommers of its presence. Matzu's tribe arrives to give him a burial and prepare Mattley for battle against Balacau. After a series of traps fails to do much damage, Mattley acquires a rocket launcher from Sommers and kills the creature by firing an explosive into its mouth. He and Sommers grow close at the bottom of a waterfall as the natives cheer and CIA rescue helicopters arrive.
