Nyssa, portrayed by Sarah Sutton, traveled with the Doctor between Keeper of Traken and Terminus.
Nyssa was the aristocratic daughter of Counsel Tremas, who had been chosen to become the next Keeper (a position of great importance). The Master planned to use Tremas’s investiture to give him a new regeneration cycle, and was renewed when he merged with Tremas, robbing Nyssa of her father.
Orphaned, Nyssa was soon reunited with the Doctor, and they traveled together, with Adric, Tegan and Turlough, for some time, before arriving on Terminus. Here, Nyssa was infected by lazar’s disease, and decided to stay behind, to help the Vanir research a cure.