In the conclusion of the four-part story "Robot," the members of Think Tank have hidden themselves in a bunker, preparing for the nuclear holocaust which they themselves have planned. It falls to the Doctor (Tom Baker) to shatter Think Tank's dreams of world domination. But is the Doctor, now encased within a new body and endowed with a whole new personality, up to the present challenge? Ian Marter joins the regular cast in the role of Harry Sullivan. First telecast on January 11, 1975, "Robot, Episode 4" was written by Terrance Dicks. ~ Hal Erickson, Rovi