The Port of Missing Men by Meredith Nicholson

Shirley Claiborne is fascinated by the tall handsome man named John Armitage who seemed to follow her and her brother, Captain Claiborne, as they traveled around Europe. Count von Stroebel had urged Armitage to do something for Austria. Now von Stroebel was dead – cut down by an assassin’s bullet – and Jules Chauvenet is one step closer to seeing the corrupt and worthless Francis ascend to the throne. When Shirley and Captain Claiborne sail for their home in Washington D.C., Armitage follows them. Monsieur Chauvenet also follows, but is he following Shirley or the mysterious John Armitage? And just who is John Armitage? (Introduction by MaryAnn)