The Doctor, Sarah and Harry arrives on the Nerva Beacon, hoping to find the TARDIS waiting for them, instead the intrepid trio find a space station in the grip of a deadly plague that has wiped out most of its crew. But the Doctor soon comes to suspect that the 'plague' is no natural illness – and that some of his oldest and most fearsome foes are behind it... The beacon has been set up to warn space traffic of a new satellite orbiting Jupiter, but one craft is taking no notice of the order to stay clear – a Cybership. The satellite is Voga, Planet of Gold, home to the seemingly harmless Vogans – but why are the Cybermen so determined to destroy it? Without the TARDIS, the Doctor is unable to return Sarah and Harry to the 20th Century. But then Sarah falls victim to the mystery virus, and unless the Doctor can find a cure – quickly – she will never make it home at all