The Face of Eve by Betty Burton
When Eve left her home town of Portsmouth, she'd never intended to return. Poor housing, poor wages and poor opportunities forced her to make a clean break. But the experience gained as a driver in Spain, desperately fighting for the Republic, enabled her to reinvent herself and to gain a confidence and maturity far beyond her years. She has become her own woman. Which makes her a very attractive propsect in more than one sense to David Hatton, who is charged with selecting highly unusual, independent and intelligent candidates for the Special Operations Executive. This mysterious woman from his past is obviously suitable - as is her current lover, a captain from the Soviet Secret Service. For in the war that lies ahead, one thing is certain: brute force won't be enough.