The Interloper by Sullivan Clarke
When Gretchen Altman's husband Benjamin dies in an accident, she is left alone to raise their young son and run the horse farm he started with borrowed money - or so she thinks. On the day of the funeral, a stranger appears and lays legal claim not just to the farm but to Gretchen and her young son as well.
Kane Altman claims to be her late husband's brother, but Gretchen realizes he is as different from Benjamin as night is from day. Where Ben was short, fair and gentle, Kane is tall, dark and stern. He has definite ideas about how a wife should behave and makes it clear that he will enforce his authority with corporal punishment should she defy him. For a headstrong woman like Gretchen, adjusting to the new rules and expectations will not come without painful consequences. But even as she struggles to obey, she is plagued by doubts. Kane Altman is keeping something from her, and she soon begins to doubt that he his who he claims to be.