She was actually Lantis from the planet Imafiya, on a research mission when she was separated from her companions. She had been stranded on Earth since 1995, having been unable to repair her broken recall device due to the comparatively primitive nature of human technology. She responded to the ad for a travelling companion to try and track down the man who had actually placed the ad, with the goal of capturing him for the bounty, but the Doctor was able to convince her that he wasn't the man she was looking for. He subsequently repaired her recall device and allowed her to return home. (AUDIO: Situation Vacant)