- You may be looking for Jane Blythe (The Sea Devils).
Jane Blythe was the secretary of Vanessa Laing-Rabdall, working in Lexington Bank. She accompanied the tour around the building. Amy noticed that she was very nervous, as if waiting for something to happen. When Brian Edelman died, she explained that it was overwork and the bank had advised against this.
After the Blenkinsop and Symington invasion, she revealed herself to be the enemy, who had been persistent in equipping the workers with Time Harvesters and making sure that Lexington Bank held a prominent status in the economic market. When Amy was tricked into acquiring a Time Harvester, with her subsequent "loan" of four days' worth of time leaving her with over twenty-five years' worth of interest, the Eleventh Doctor took on Amy's debt to expose his status as a Time Lord. Excited at the possibilities, Jane took him to the Time Market to try and auction him off, but while she was occupied the Doctor's allies damaged the structure she was using to store the Time she had harvested, limiting the temporal resources Jane had to draw on.
With Jane unable to stop the Doctor saying anything she didn't want him to say, the Doctor revealed that Jane had lied to the rest of the Market; in order to convince the Market that she could pay off the temporal collateral needed for her plan, she had claimed that 100,000 years was merely a tenth of the total human lifespan, until the Doctor convinced those at the Market to check Earth's information networks and see the truth for themselves. With faith in the system having collapsed, Jane was erased from existence as she lost the Time she had used, the Doctor buying the last shares in the market so that he could restore the stolen time to his allies. (PROSE: Borrowed Time)