Everyone knows that Pluto is a barren airless rock. So naturally the Fourth 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.