Everyone who looks at "The Daughters of Edward Darley Boits," the grand-scale painting by John Singer Sargent that hangs in Boston's Museum of Fine Arts, is drawn into its mysteries. Who are these four girls, dressed in prim pinafores? Why is the composition so far off balance? Why are two of the girls cloaked so completely in shadows that their "portraits" are little more than ghostly ciphers? Author Douglas Rees explores the complexities of this masterpiece with a psychological thriller that lets Sargent himself tell the story behind the canvas. When one of the girls scratches the words "HELP US" on a scrap of drawing paper, Sargent realizes that he alone has the power to save them. Will the great portraitist paint the girls as they appear—or will he show the reality of their dark, mysterious lives?