Lieutenant Sam Bishop is finishing an assignment in Bangkok when he receives a call from Kate Stewart. She has a new job for him - hunt for a stray Nestene energy unit that has come down somewhere in the Gobi desert.

In Mongolia, Sam is joined by Osgood and they set off into the Gobi. But there are Autons in this desert. They are also looking for the energy unit, and they're ready to kill anyone who comes into contact with it.

Back in London, Kate is becoming suspicious of Simon Devlin's company, and decides to pay him a visit.