The ghosts of Paris : a novel / Tara Moss.

Enhanced descriptions from Syndetics:

A thrilling tale of courage and secrets set in postwar London and Paris, in which a search for a missing husband puts investigator and former war reporter Billie Walker on a collision course with an underground network of Nazi criminals

It's 1947. The world continues to grapple with the fallout of the Second World War, and former war reporter Billie Walker is finding her feet as an investigator. When a wealthy client hires Billie and her assistant Sam to track down her missing husband, the trail leads Billie back to London and Paris, where Billie's own painful memories also lurk. Jack Rake, Billie's wartime lover and, briefly, husband, is just one of the millions of people who went missing in Europe during the war. What was his fate after they left Paris together?

As Billie's search for her client's husband takes her to both the swanky bars at Paris's famous Ritz hotel and to the dank basements of the infamous Paris morgue, she'll need to keep her gun at the ready, because something even more terrible than a few painful memories might be following her around the city of lights . . .