Theodosia Middlemint

 was a lady and sister of Geoffrey Balsam. She owned Sarah as a slave. She invited the Sixth Doctor, Constance Clarke and Flip Jackson to the grand ball. The Doctor took a shine to her. She found Flip after she escaped from Titus Craven but sent her back to him when he arrived. Flip and the Doctor gave her confidence and she confronted her brother having discovered that he had stolen her inheritance. (AUDIO: The Behemoth)