On an old Earth colony, Tegan is a captive of Anna in a little room. Anna is the only survivor of her colony, which had been attacked by aliens. She has been alone for a long time. Anna ties Tegan to a chair to keep her from leaving with the Doctor and Nyssa in the TARDIS. Exploring the corridors, the Doctor and Nyssa find the crashed remains of a spaceship. They think that Tegan and Anna are doing "human things", and are unaware that Tegan is a prisoner.