One summer morning, at the end of a dirt road in the thick western forests, a team prepares for a three day hike into the deep woods where no one has ventured before.  The team consists of two paleontology professors, Dr. Ethan Edwards & Dr. Helen Gilbert, one of their graduate students, Louise Keaton, four Forest Rangers-- Charles Landon, Spencer Combs and his sister Janet, Brian Stratton-- and an ex-Forest Ranger named Roger Gordon.  Their goal is to find fossils that will confirm the existence of an ancient primate that flourished in China but was not thought to have migrated to North America.

On the third night of the trip, with only a few miles to go until they reach their target site, they camp out in a clearing.  The next morning they awaken to an amazing surprise: this is no ordinary clearing; it’s some kind of graveyard!  The scientists are beside themselves with joy—they never expected to be so lucky.

But their luck turns bad, as one of the Rangers disappears and another is attacked by an unknown creature while searching for him.  Since the safety of the civilians is their number one priority, the Rangers order the team to head home.  But as they hastily make their way back to the main road, they come to realize that they are being hunted by the creature, an eight foot tall gorilla-like animal that walks upright.  One by one the team members are plucked away and viciously killed.

Who will survive the night?