After the world's population has been ravaged by a pandemic, a man lives a lonesome existence in a Colorado airplane hangar with his dog and a dour gunman he has befriended. When a mysterious transmission comes through on the radio while he’s flying his old Cessna, it sparks a hunt for the provenance of the sound.
Mark 13 is a government-built killing machine programmed with artificial intelligence, able to repair and recharge itself from any energy source. Through a series of coincidences, the cyborg's head ends up in the home of a sculptress as a bizarre Christmas present from her boyfriend. Once inside its new home, the cyborg promptly reconstructs the rest of its body using a variety of household utensils and proceeds to go on a murderous rampage.