An intellectual college professor is mesmerized by the painting of a beautiful woman in a gallery window. When he, by chance, meets the subject of the alluring painting, he becomes trapped in a murder plot and witnesses his own investigation. He must now protect the temptress... Based on the novel "Once Off Guard" by J.H. Wallis./ a notorious Nazi war criminal lives a secret life as a college professor (Orson Welles) living in a pastoral Connecticut town with his lovely wife Mary (Loretta Young). After a visit from a German gentleman stranger, a mild-mannered war crimes commissioner (Edward G. Robinson), posing as an antique dealer, pays a visit to the professor and begins to unveil his previous life.