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In the conclusion of the four-part story "Underworld," the evil computer in charge of the Minyan "race bank" on the space ship P7E is determined to prevent future Minyan procreation by destroying the sister ship R1C. Since both the Doctor (Tom Baker) and Leela (Louise Jameson) are on board the R1C, it is imperative that he prevent this catastrophe. To foil the computer and its robotic servants, the Seers, the Doctor again relies on his own quick-wittedness and ability to mentally outmaneuver his enemies. First telecast January 18, 1978, "Underworld, Part 4" was written by Bob Baker and Dave Martin.