Doctor Who and the Sunmakers — Terrance Dicks

Everyone knows that Pluto is a barren airless rock. So naturally the Doctor is surprised when he discovers artificial suns, an ultra-modern industrial city and a group of colonists being worked -- and taxed -- to death in this inhospitable and supposedly undeveloped part of the universe...

With the help of his companion Leela and the faithful K9, the Doctor takes on the mysterious and powerful Company, ruthless exploiter of planets and their people.