An extraterrestrial spacecraft deploys a shuttle to Earth. Sometime later, Alan "Dutch" Schaefer and his elite paramilitary rescue team—skilled mercenary Mac Eliot, explosives expert Poncho Ramirez, macho Blain Cooper, expert tracker Billy Sole, and jokester Rick Hawkins—are tasked with rescuing a local cabinet minister whose helicopter was shot down in a Central American jungle. Dutch's Vietnam War ally, Al Dillon, now a CIA agent, accompanies the team to oversee the mission.
The team find the helicopter wreckage and traces of guerrilla soldiers, as well as three skinned corpses hung high in the trees nearby. Dutch identifies the corpses as Green Berets, and becomes suspicious of Dillon's intentions after learning the helicopter was outfitted for surveillance. Dutch's team attacks the guerrilla camp, killing the soldiers and their Russian military allies, and learning the hostages were CIA agents. Dillon admits the cabinet minister story was a lie to convince Dutch—who refuses to use his team for assassinations—to eliminate the camp and prevent a Soviet-sponsored invasion. Dillon also discloses that the original mission team disappeared and the Green Berets had been sent to find them. Dillon takes a surviving guerrilla, Anna, prisoner, and the team travels towards the extraction point.
Unbeknownst to the team, a technologically advanced, humanoid predator has stalked them since their arrival, remaining invisible with a cloaking device, and using thermal imaging vision to see their body heat. Billy senses the presence of something inhuman, but cannot confirm his suspicions. Anna flees when the team is distracted, and although Hawkins catches her, he is killed by the predator while Anna is spared. As the team searches for Hawkins' body, the predator kills Blain. Mac catches a glimpse of the predator's cloaked form and, enraged at Blain's death, provokes the team into blindly firing their weapons into the jungle, wounding the predator. The team sets up camp for the night, booby trapping the perimeter. A wild boar triggers a trap, and the predator uses the ensuing confusion to steal Blain's corpse.
The following day, Dutch deduces that the predator is stalking them from the treetops. Dutch releases Anna, needing her to work with them to survive. She recounts local folktales of a monster that kills men and takes trophies from their corpses, typically when the weather is hot. The team booby trap the treetops to force the predator into a net, but it is able to escape and Poncho is injured. Mac and Dillon, who both want to make amends to the team, pursue the predator, but they are outmaneuvered and killed. The predator soon catches the survivors, killing Billy and Poncho. Realizing the predator only attacks those it considers a threat, Dutch warns Anna to relinquish her weapon and run to the extraction point. Dutch distracts the predator before falling from a cliff into a waterfall and washing up on a muddy shore. The predator pursues Dutch, but is seemingly unable to see him, and leaves to collect the skulls of the others as trophies. Dutch concludes that the mud masked his body heat, making him invisible to the predator.
Seeking to avenge his team, Dutch creates makeshift traps and weapons. As night falls, he covers himself in mud, lights a fire, and lets out a war cry to lure the predator to him. Dutch uses his invisibility to wound the predator and disable its cloaking device, but falls into a river which washes off his mud camouflage. Deeming Dutch a worthy opponent, the predator removes its weapons and mask—revealing a monstrous visage—to face him in hand-to-hand combat. Easily outmatched by the larger and stronger creature, Dutch attempts to goad it into a trapped tunnel, but the predator suspects his plan and circumvents it. Dutch triggers the trap himself, releasing its counterweight, which crushes the predator. Mortally wounded, the predator activates a wrist-mounted self-destruct device. Dutch flees, barely escaping the enormous resulting explosion that razes the area.
As dawn breaks, the extraction helicopter arrives with Anna to collect the exhausted and traumatized Dutch.