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In the third episode of the four-part story "Frontios," the titular planet has become the new home for the crew of the TARDIS, as well as a group of survivors from a nuclear holocaust on planet earth. But all is not tranquil for the new arrivals, thanks to the presence of a hyperintelligent insectoid race called the Tractators. Having burrowed beneath the planet's surface, the Tractators intend to convert Frontios into their own private space vessel -- which of course will spell the doom for everyone else in the vicinity, including the Doctor (Peter Davison). Originally telecast on February 2, 1984, "Frontios, Episode 3" was written by Christopher H. Bidmead.