Honestly, the cover grabbed me. The World War II planes in the red and white stripes; the female heroine pilot looking off in the distance; and the title implying the secrecy, adventure, and danger of being a spy on foreign soil during wartime conspired to entice me to pick the book up. The literary style is focused on plot, so it is an easy, fast-paced read. However, I did enjoy learning new aspects of World War II that I had not previously known: the Freedom Line, WASP (Women Airforce Service Pilots), and the OSS (Office of Strategic Services) - the predecessor of the CIA. The author combines family experiences, actual history, and creative fiction to weave a tale of suspense.
NOTE: I did not know upon check-out that this is the third book in a series, but it's still a good read on its own.