Humanity has spread out and colonised nearby star systems but a plague in 2150 led to the colonies being abandoned and left to their automated robotic maintenance systems. While several of these colonies have been successfully re-inhabited, the colony on the planet Tau Ceti III (orbiting the star Tau Ceti) has been uncontactable since a meteor smashed into the planet. A mission sent to Tau Ceti III in 2164 landed on the planet but broadcast a mayday message followed by silence. Experts decided that the planet's robots were running amok as a result of the meteorite impact. The only chance, it was decided, of successfully stopping the defence systems without destroying the cities already there is to send a single pilot in an armoured Gal-Corp skimmer to the planet's surface with the task of shutting-down the central reactor in Tau Ceti III's capital, Centralis.