Kate Rees is an agent with British Intelligence.
She definitely does not plan on working in that occupation and, truth be told, she is not, really. She might be better considered a voluntary conscript in that life shoved her into it. It, in this case, is Section D, "a group [that] does not exist officially". As Stepney, the man who recruits her puts it, "all our operations are deniable. But I never told you that".
The year we first meet her is 1940, the location is Paris, France, and the occasion is the attempted assassination of the German Fuehrer, Adolf Hitler, while he was paying an abbreviated visit to that just recently conquered city. The visit was short-lived, according to these adventures, because Rees just narrowly missed putting a bullet into his head from a distance, wounding the man standing behind Hitler because at the moment of the sniper rifle trigger pull, the leader bent to pick up a little girl in the crowd.
I am not giving much of a spoiler here, by the way. This is information presented to us in the first page of the first recorded adventure. The rest of that adventure's contents will be the lead-up to the attempt and, even more harrowing, its aftermath.
Rees is an American, living on the Orkney Islands with her Welsh husband, Dafydd, and their 18-month-old daughter, Lisbeth, in the fall of 1939 when a Luftwaffe attack on a nearby British naval vessel would cause tremendous loss of life and considerable confusion in its aftermath and in that confusion, a terrible accidental explosion would take the man and the girl from her. The next eight months would be one of grief and just holding on.
And then would come the chance that would give Rees some hope of vengeance as well as the reason for her membership in this compendium. Rees, we learn early on, is an incredible shot with a rifle, an expert sniper whose only training had come at an early age. "I grew up on ranches in Oregon. My father taught me to hunt when I was a little girl." That is what she tells her supervisor in the testing facility on the island where she worked. Her job there was to test-fire randomly chosen Lee-Enfield rifles to ensure they were ready for duty. Her uncanny marksmanship would be noted by that man and he would offer her a better job. She declined then for family reasons. Now bereft of that family, she makes a call and her life will change yet again.