The Doctor (Jon Pertwee) discovers trouble on Peladon when he returns 50 years after his last visit. Oppressed miners are rebelling, clashing with the ruling class -- and everyone's spooked as images of their deity, Aggedor, begin appearing and killing miners. Aided by Sarah Jane (Elisabeth Sladen), the Doctor investigates the mysterious murders and tries to help Queen Thalira set things straight in this episode of the sci-fi action series.