Rosie Ewing is an agent with the British SOE.
That is the designation for the Special Operations Executive, the department responsible during the Second World War for conducting espionage and sabotage in the Nazi controlled region of Europe. [Created in 1940, it existed until the war was over and was officially disbanded in 1946.]
In her first recorded adventure (well, first published) she is about to embark on her second offical mission, this one taking her into France to be a "pianist", cover term for a radio operator working with the Resistance and other embedded operatives. She is in her mid-20s and was already a widow, having lost her husband Johnny. She has mixed feelings about the late fellow operative considering that she had loved him enough to marry him and mourn him but still bitter about the fact that she had learned he was not as true to her as she was to him.
But it is wartime and Ewing definitely feels she must do her part even if that means heading into enemy territory to do a job for which many others lasted less than two months. Given the cyanide pill that all her colleagues were provided, she has to ponder if she would have the courage to take it when the time came or if she might take it too soon.
As the series progresses, her assignments will get more dangerous as she proves herself capable of more than first thought. She will pay dearly for her convictions and her successes, though. But the idea of stopping and just staying at home to be save never really occurs to her.