The Doctor arrives on a planet where two tribes, the savage Sevateem and the technically brilliant Tesh, are at war. He meets Leela, an exile from the Sevateem, and discovers that the tribes' god of evil is apparently himself...
Arriving on Space Station Nerva in its distant past, the Doctor, Sarah and Harry find its crew threatened by a mysterious plague. Discovering that things are not as they seem, they uncover a Cyberman plot to destroy Voga, planet of gold.
When the TARDIS lands in a quarry on Earth, Sarah unearths what appears to be a fossilised hand, buried in one-hundred-fifty-million-year-old strata. Analysis shows the hand to be silicon-based and inert, but when Sarah begins to act as if possessed, the Doctor suspects that it may still be alive...
