The English Wife by Lauren Willig

In 1899, Janie Van Duyvil's life is turned upside down when her brother, Bay, is found stabbed to death, and her sister-in-law, Annabelle, is presumed drowned. With the Van Duyvils' wealth and social standing, the press is having a field day speculating that Bay killed Annabelle then himself. Janie--never married and without a good relationship with her mother--decides to delve into Bay's and Annabelle's marriage to uncover the truth, with the help of a reporter named Mr. Burke. The English Wife recounts in flashbacks Bay's and Annabelle's courtship and subsequent marriage, along with Janie's journey to find out what really happened to her brother and his wife.