Knowing that Noah has been infected by the Wirrn, the Doctor persuades Vira to halt the reviving of her people, knowing it will place them in danger as well.

The Doctor, Sarah and Harry teleports to Earth to ensure the planet is safe for the survivors on-board Nerva Beacon to return to Earth and re-inhabit their world. Only to find a Sontaran named Styre has captured a group of humans and conducting experiments on them to discover the human body's weaknesses, as part of the Sontaran's goal for domination of the galaxy.