The Earth colony on Yemaya 4 is a very ordinary place. The colonists spend their time farming, building homes, raising families. But when the Doctor and his companions arrive they find a virus sweeping through the population, unleashing the colonists’ latent psychic powers. The Doctor and Chris fall prey to the infection, and discover telepathy is not the only symptom. Chris is unable to resist the call of an ancient place of sacrifice, while Roz and Benny travel back in time to the origin of the virus, and uncover a desperate bid for immortality.