The Queen's Accomplice (A Maggie Hope Mystery, Bk. 6)

Spy and code-breaker extraordinaire Maggie Hope returns to war-weary London, where she is thrust into the dangerous hunt for a monster, as the New York Times bestselling mystery series for fans of Jacqueline Winspear, Charles Todd, and Anne Perry continues.
 
England, 1942. The Nazis' relentless Blitz may have paused, but London's nightly blackouts continue. Now, under the cover of darkness, a madman is brutally killing and mutilating young women in eerie and exact re-creations of Jack the Ripper's crimes. What's more, he's targeting women who are reporting for duty to be Winston Churchill's spies and saboteurs abroad. The officers at MI-5 quickly realize they need the help of special agent Maggie Hope to find the killer dubbed "the Blackout Beast." A trap is set. But once the murderer has his sights on Maggie, not even Buckingham Palace can protect the resourceful spy from her fate.