The Woman in The Fifth, by Douglas Kennedy
Harry Ricks is a man who has lost everything. A romantic mistake at the small American college where he used to teach has cost him his job, his marriage, and the love of his only child. Hounded by scandal, he flees to Paris, where a series of accidental encounters lands him in a grubby room with a job as night watchman for a sinister operation. Just when he begins to think he has hit rock bottom, romance enters his life in the form of Margit—a cultivated, widowed Hungarian émigré who shares Harry’s profound loneliness but who keeps her distance, remaining guarded about her past. As Harry wrestles with Margit’s reticence, he begins to notice that all those who have recently done him wrong are meeting unfortunate ends—and it soon becomes apparent that he has stumbled into a nightmare from which there is no escape.