Doctor Who is a long-running British science fiction television series featuring The Doctor, a Time Lord from the planet Gallifrey whose adventures see him travel through time and space. Over the years, different actors have starred in the role, and to compensate for the realities of the television business Time Lords were given the ingenious ability to regenerate their bodies when they die.
Underworld is the 96th story of the Doctor first broadcast in four weekly parts from January 7th to 28th, 1978, on BBC 1. "Part One" finds the Fourth Doctor (Tom Baker) joined by companions Leela (Louise Jameson), a primitive Sevateem warrior descended from an Earth colony ship, and K-9, his robotic dog, as the TARDIS appears on the R1C, a spaceship belonging to the Minyans, a species the Time Lords encountered 100,000 years ago, which ultimately resulted in the Time Lords enacting a non-intervention policy, though obviously not all observe it. Led by Jackson, the crew members of the R1C have been traveling for just about that long regenerating their bodies. Their quest is to find the P7E, a sister ship that left their homeworld before them and contained the DNA banks of the Minyan race, which were to be used to populate a new planet.
The P7E's signal sends the R1C to a planet where the populace known as the Trogs lives underground, works like slaves, and is ruled by the Oracle, a cruel leader who controls the Trogs' numbers by causing things to fall from the ceiling in people. The Doctor takes on multiple tasks as he works to help both the Minyans and the Trogs, which he does a little too easily. The manner of the Oracle's eventual defeat is unbelievable considering it basically falls for its own trick.