Lynn Pickering

 was a student at St Matilda's College in 1977. She saw the three mysterious nuns at a choir practice. She later saw one in her dormitory. After her disappearance, Megan Matthews told the Fourth Doctor that she had been researching the college. She was placed into an alien spaceship as a pilot but the Fourth Doctor managed to remove her. Megan later tried to coerce Lynn back into the machine. The Doctor managed to get her out of the machine before the ship exploded. (AUDIO: The Cloisters of Terror)