Nyssa and the Doctor are reunited with Tegan while fighting Omega in Amsterdam and on Gallifrey. Later, they help Tegan battle her inner demons (personified by the Mara), and in the events of Mawdryn Undead they meet the Doctor's old friend and ally Brigadier Lethbridge-Stewart. It is during this adventure that the TARDIS crew adopts Turlough, an alien posing as a pupil at an English boarding school, who has secretly entered into a bargain with the Black Guardian to assassinate the Doctor. His interference with the TARDIS infrastructure destabilises it and it locks onto a seemingly derelict space station, Terminus, separating Nyssa from the others. Nyssa's adventures with the Doctor come to an end here, as – to Tegan's horror – she elects to stay to help free the enslaved guards and turn the station into a real hospital. The Doctor is moved by this noble gesture and parts saying that he thinks she is very brave. Nyssa's deep affection for the Doctor is demonstrated at this point when she kisses the Doctor goodbye.
