A young woman who acted as an agent for Harold Saxon. She befriended Francine Jones, Martha Jones' mother, and monitored phone calls which her daughter made to her whilst she was travelling with the Doctor. On the day after his election as Prime Minister, Saxon had her attempt to ensnare Martha - using her father as well as her mother to try to talk her into visiting their home where she could be captured. When Martha's father shouted out a warning, he was arrested, and Saxon gave Miss Dexter orders for the whole family to be rounded up.
Played by: Elize du Toit. Appearances: 42, The Sound of Drums (both 2007).
- She is credited only as "Sinister Woman" for both episodes, but du Toit was told that this was her character's name.