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.
Set in a future Earth (2035 A.D.) where robots are common assistants and workers for their human owners, this is the story of "robotophobic" Chicago Police Detective John Spooner's (Smith) investigation into the murder of Dr. Alfred Lanning (James Cromwell), who works at U.S. Robotics, in which a robot, Sonny (Tudyk), appears to be implicated, even though that would mean the robot had violated the Three Laws of Robotics, which is apparently impossible. It seems impossible because.. if robots can break those laws, there's nothing to stop them from taking over the world, as humans have grown to become completely dependent upon their robots. Or maybe... they already have? Aiding Spooner in his investigation is a psychologist, Dr. Susan Calvin (Moynahan), who specializes in the psyches of robots.