To get away for the weekend, five college students (Dana, Curt, Holden, Jules, and Marty) travel to Curt's family cabin. Things start getting ... weird ... after Dana reads Latin incantations from an old diary in the basement. Specifically, zombies start attacking them.
Simultaneously, two engineers, Sitterson and Hadley, have been engineering these horrifying events on behalf of a shadowy organization at a site only known as the Facility, led by the Director.
Over the course of the film, it's revealed that the Facility sacrifices five classic archetypes from slasher movies (the virgin, scholar, fool, jock, and the promiscuous one), annually in order to keep a group of ancient monsters, the Ancient Ones, from destroying the Earth.
Spoiler: Instead of killing her friend Marty, Dana (the "virgin"), decides to let the world end, because humanity's not worth saving.