In the conclusion of the four-part story "Pyramids of Mars," it appears as though Marcus Scarman (Bernard Archard) has killed the Doctor (Tom Baker), whose mind was being controlled by the spirit of Osirian master criminal Sutekh (Gabriel Woolf). Does this mean that Sutekh will succeed in his efforts to destroy both Mars and Earth, and thereby regain his freedom? The key to the denouement of this episode is a little something known as "time differential." Written by Stephen Harris, "Pyramids of Mars, Episode 4" first aired on November 15, 1975. ~ Hal Erickson, Rovi