The Doctor, Sarah Jane and Harry teleport to Earth to ensure the planet is safe for the survivors on board Nerva Beacon to return and reinhabit their world. A Sontaran named Styre has captured a group of humans and is conducting experiments on them to discover the human body's weaknesses, as part of the Sontaran's goal for domination of the galaxy.
Quest roles:
Terry Walsh(Doran (uncredited)), Donald Douglas(Vural), Glyn Jones(Krans), Peter Walshe(Erak), Peter Rutherford(Roth), Kevin Lindsay(Styre / The Marshal)