The TARDIS arrives in the future on the planet Pluto where there are now six suns, a breathable atmosphere and a large industrial community. The Company controls the planet and exploits the workers, pays them a pittance and then taxes them on everything imaginable. The Doctor and Leela join forces with an underground band of rebels led by a man named Mandrel.

They learn that the head of the Company's operations on Pluto, represented by the human official Gatherer Hade, is an Usurian known as the Collector. The Usurians enslave planets through economic means and then fleece the inhabitants with exorbitant taxes. The Company keeps the citizens in line by diffusing a calming gas, PCM, through the air conditioning system.

The Doctor manages to stop this, and the workers then rise up against the Company and hurl Gatherer Hade to his death from the roof of a tall building. The Doctor meanwhile gains access to the Company computer and programs it to apply a two per cent growth tax. The Collector, unable to cope with the loss of his profits, reverts to his natural form - a type of poisonous fungus - and is rendered harmless.