Armistice Day. November 11th. A date I’ve known all my life and commemorated annually with a red poppy in the buttonhole as long as I lived in England; commemorated—without really understanding its meaning until I started to write about the 1920s. I’ve learned a lot about the first world war in the 20 years since. Though I decided not to make its horrors the focus of my series, I soon realized that two subjects that attracted me to the period were inextricably linked to the war. First, the country could not afford the extravagances of fashion, so women’s clothes became much simpler and more comfortable; and second, the huge loss of life in the trenches helped open an unprecedented range of careers to women. The more I learned, the more careful I had to be to pick and choose what information I used in my mysteries, especially as they’re basically lighthearted. We’ve all read (or started to read) novels where the author has attempted to cram in every scrap of extensive research. Noth...