The Fourth Doctor and Sarah Jane are on Farrash, posing as the Earth delegates to the Farrash Future Ratification. The people of Farrash are slowing dying out, due to a change in solar radiation. This is slowly causing the people to become sterile. Different factions on the planet are doing research to save the population. One group, supported by the Leader, is aborting the foetuses of volunteers and will use the brain matter to animate metal bodies. The Farrashians have dozens of legs, and only their brains can perform the complex motions required to make the legs function and move.