Caxton

 was the matron of Kenstone Hall.

She was taken over by the Nurazh that brought to Earth. The Nurazh possessing her then betrayed the Master. She fought the Third Doctor at the top of the Hall, with both falling several stories to the ground below. Miss Caxton died from the fall, and the Nurazh left her for the Doctor. (PROSE: The Touch of the Nurazh)