Doctor Izard by Anna Katharine Green

From the publisher

The opening scene takes place in a hospital ward where two patients lie, apparently dying, when a man enters and offers a proposition to one of them. The story then shifts to another town where, years earlier, Polly Earle’s mother died of unknown causes and her father disappeared, leaving Polly, a small child, parentless and penniless. Raised by neighbors, Polly is now a beautiful young woman engaged to be married. A stranger arrives and makes an unsettling request of Polly. Doctor Izard, an intensely private person who had attended her mother, becomes involved. Anna Katherine Green, a prolific and popular mystery writer, was considered to be "The American Agatha Christie".