Anthropological professor Conrad Hamilton attempts to study a new species of primate in Thailand; looking for the missing link between humanity and the great ape. His team dies trying to catch one for study. Hamilton and his assistant Chenne are the only survivors. Meanwhile, college anthropology students are flown into a remote region of the Asian jungle and picked up by a guide. He drops them off at the edge of a road, but refuses to go further, as "bad things" are in there. After reaching the trail's end, the students set up camp. At night, the creature attacks, but Chenne appears and scares it off with a flare. Chenne escorts the students to Hamilton's camp. The following day, Hamilton mentions an uncharted valley within the jungle and its potential for career-launching documentation. He has Chenne confiscate the students' mobile phones and hand out information bracelets for each member containing their emergency contact info. Then, he leads the team to the valley entrance. The group rappels down the cliffside and into the valley, injuring Josh in the process. On the first night in the valley, Hamilton passes around a skull which belongs to the primate. The students cannot identify the skull, which is nearly twice the size of any known human or primate cranium. They are interrupted by a bloody survivor from the original research team. Hamilton and Chenne care for the man, who eventually dies. Hamilton thinks that the creatures let him go as a warning. During the night, Sydney visits the outhouse, only to be dragged away into the jungle. The next morning, Hamilton announces that Sydney came to him scared and wanting to go home, so Hamilton had Chenne take her out of the jungle. Meanwhile, Chenne drags Sydney through the jungle and leaves her battered and beaten. Sydney eventually stumbles into a creature that kills her. The team continues to follow Hamilton and Chenne. Hamilton is secretly tracking each student by a hidden chipset in their bracelets. The students resolve to steal Hamilton's AK-47 and gain control of the situation. Seth begins leaving a trail through the jungle by tying off pieces of cloth to trees. At night, while the students begin to fashion their plan for the following day, a foul-smelling rain begins pouring down on their tents. Just as they recognize the smell as urine, Josh is yanked out of his tent and dragged up into the trees. The team scatters and begins following Josh's screams through the jungle. As Greg attempts to save Josh, Chenne accidentally shoots him, but then proceeds to tie him to a tree as bait. She camps out nearby with her gun. One of the monsters eventually sneaks up on Chenne and kills her before mauling Greg. Hamilton runs across Seth during the chaos and knocks him unconscious. Hamilton locates the two remaining students, Dani and Amy, and orders the former to document everything with her video camera. Believing themselves to be the only survivors, both girls are forced to obey Hamilton. He tracks Sydney's bracelet and finds it still attached to her severed arm, dangling from a tree. Hamilton examines an apparent rigging done to the tree, only to spring a trap that results in bamboo shoots impaling him through the back. After he dies, the girls return to their campsite, only to find it cleared of their tents and equipment. They keep running while the monster seems to be following them. Dani is eventually killed, leaving only Seth and Amy standing. They reach a cave and see Seth's entire cloth trail assembled and attached to the opening. Inside the cave, Seth is killed. Amy sheds light on one of the monsters for the first time, revealing it to be a
large ape with a bloody set of fangs. More apes appear, and Amy screams in terror before one of them kills her. ==Cast==