“Underworld” is an adventure of the fifteenth season of “Doctor Who” classic series which aired in 1978 featuring the Fourth Doctor and Leela. It follows “The Sun Makers” and it’s a four parts adventure written by Bob Baker and Dave Martin and directed by Norman Stewart.

The Fourth Doctor (Tom Baker) brings Leela (Louise Jameson) to the edge of the universe, where they encounter a Minyan starship, whose crew has been looking for the other survivors of their planet for a hundred thousand years, especially for the genetic bank of their species they could use to give their civilization a new beginning.

The Minyan starship enters a nebula in which the crew localized the signal from the other survivors but the material that compose it is attracted to the ship forming a planetoid around it. At the center of the planetoid they find the other Minyan spaceship and discover that they use the rocks to create fuel and food but most of the population are slaves.