Bellewether / Susanna Kearsley.

Secrets aren't such easy things to keep: It's late summer in 1759, war is raging, and families are torn apart by divided loyalties and deadly secrets. In this complex and dangerous time, a young French-Canadian lieutenant is captured and billeted with a Long Island family, an unwilling and unwelcome guest. As he begins to pitch in with the never-ending household tasks and farm chores, Jean-Philippe de Sabran finds himself drawn to Lydia, the daughter of the house. Slowly, Lydia Wilde comes to lean on Jean-Philippe, a true soldier and gentleman, until their lives become inextricably intertwined. Legend has it that the forbidden love between Jean-Philippe and Lydia ended tragically, but centuries later, the clues they left behind slowly unveil the true story.