City of ghosts
(Book)

"Working in San Francisco as a PI years [after her work in the Spanish Civil War, World War II seems] a world away, but it might as well be on [Miranda Corbie's] doorstep now that she's learned that her mother--whom she hasn't seen in years--is trapped in England. There isn't much she can do until the State Department asks her to keep an eye on a chemistry professor who they suspect is a Nazi spy trafficking in information on allied forces armaments. The five grand fee that the State Department is offering for the job is tempting, but what seals the deal is the chance to bring her mother home"--,Provided by publisher.