Isadora Fleming is an agent with MI-6.
She prefers to call it the Secret Intelligence Service and corrects those who call it MI-6 but regardless of the name, that is the organization for which she has proven to such a valuable asset. She is not a spy and would chuckle, or frown, at someone making such a suggestion. She has no interest in being one for she knows what she is good at and she will stick with it.
She kills people.
Fleming was born Isadora Minerovich of the small Eastern European nation of Serezovnia ruled with an iron fist from the Soviet leadership in Moscow. Her father was one of a revolutionary band who was murdered by a General Presnyakov of that nation's secret police. When her mother objected, she was killed as well. In the next room, a frightened five-year old Isadora awaited her own death. The soldier ordered to seek her out and kill her took pity on the little girl and took her to safety. After a while she was eventually smuggled into the U.K where she was adopted her and her last name changed so no one from her previous country could track her down.
We meet her when, after a brief recap of what was mentioned above, she is in the British military, age 21. Despite what her instructors would tell her, she was proving an excellent student and her abilities, plus her background, brought her to the attention of a talent scout for the SIS, a major piece of work named Broadbent. He offered her a position and she took it.
She would continue to work for Broadbent, growing to distrust and hate the man more and more, for quite a few years before the coming of the apocalypse. The zombie apocalypse.
After that, things get very, very strange.