The Pirate Planet is not an episode that only die hard Doctor Who fans should watch. Written by Douglas Adams, this second episode in the Key to Time sequence is full of the humor one would expect if one is familiar with his other writing. It features not only the robot dog that you have already come to know and love, but also a robot parrot, and robotic dog and parrot facing off against one another. But it also has the quite sinister and scary kinds of elements that one would expect from Doctor Who even at its most frivolous.
At the heart of the episode is the idea of a hollow planet that materializes around other planets, destroying them (including all living things on them) and pilfering the wealth of gems and other valuable materials that the planet contains. There is a group that we are led to think are evil, whereas in fact they are individuals who are psychically sensitive, and thus are disturbed by the billions of deaths that result from the pirate planet they live on materializing around and destroying another, while people around them are simply delighted by the announcement from on high that another era of prosperity is beginning.
As so often throughout its history, Doctor Who offers a parable with a potent criticism of capitalist society and the ability of most people in it to simply accept that prosperity is a thing that happens, oblivious to the people out of sight whose lives are being destroyed to make them rich.