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, who began to regenerate from the fall, which killed the Nurazh when it was caught between the switch-over between the Doctor's former mind and newer mind, cancelling out the regeneration and healing him. (PROSE: The Touch of the Nurazh)