The Queen's Accomplice by Susan Elia MacNeal

In 1942, a serial killer is brutally murdering young women who work for the SOE (Special Operations Executive) in London. As an agent in the SOE, Maggie Hope takes the deaths of these women to heart, especially when she sees firsthand that the women of the SOE are not given the same rights as their male counterparts, even though their work is just as dangerous. Maggie then finds herself working with DCI James Durgin from Scotland Yard to try and find the killer, who is modelling his work on Jack the Ripper. In her personal life, Maggie awaits the arrival of her half-sister Elise Hess, whom the British government is trying to smuggle out of Germany, but the mission is fraught with danger and death to those in Elise's life. The Queen's Accomplice is the sixth book in the Maggie Hope series.