The False Faces - Louis Joseph Vance

This is the second book in the Lone Wolf series. Michael Lanyard had turned his back on his career as gentleman-thief and started a respectable life, when World War I wrecks his life. With his family dead and the spy Ekstrom alive after all, his special skills as the Lone Wolf are needed once more, this time in the war behind enemy lines. But again, there is a mysterious woman involved... (Summary by Carolin)