The marines sent to the Martian outpost are slowly eliminated as the source of the havoc is slowly revealed: the scientists working there played god as they manually added a serum to a condemned con that would give him Chromosome 24 (when a humanoid has this extra chromosome, they either become a super human or a monster…the deciding factor for which depends on if the person has psychotic tendencies). Eventually, one of the monsters makes it through the Ark and back to Earth. Sarge, Reaper, The Kid, Duke, and Samantha Grimm (Reaper’s sister) follow it back through the Ark to find savagely killed civilians everywhere. Following the killing of surviving civilians and the death of The Kid at the hands of Sarge, Duke dies as he gets pulled through a vent in the floor and Sarge is dragged off by a horde of zombies. With a bullet wound in the gut and the zombies closing in, Samantha gives her brother an injection of the serum with the 24th chromosome in order to save his life. Reaper then becomes a super human soldier, slaying every monster/zombie in sight in FPS-mode until he comes across his final obstacle- Sarge. Sarge is now slowing becoming a monster from being bitten in the neck, so a final battle between the two ensues. Essentially, “paper” beats “The Rock” as Sarge is hurdled back through the Ark and dies with the burst of a grenade. Reaper and his sis then ride the elevator up to the light as the movie ends.