Mr. Churchill's Secretary by Susan Elia Macneal (Maggie Hope series Book 1)

This is the first installment of a WWII-era spy series by Susan Elia Macneal

Summary
-Maggie Hope is not your average woman. British-born, American-raised and educated, she moves to England only to settle her late grandmother's estate. With her high level of education, she is only able to secure a job at 10 Downing Street, home to then British Prime Minister Winston Churchill as a typist, among his menagerie of cats. She's offered an opportunity to investigate the murder of a woman who worked in her position before her. As the investigation unfolds, it tells of an IRA plot to destroy England. After solving this case, she if offered the chance to undergo training for work at MI-5, or British Intelligence.