The Woman Beneath the Stairs by Christopher Greyson

Ally’s perfect marriage to Tim Hawthorne is crumbling under the weight of one trial after another. Forced to visit Tim’s mother on her secluded island off the coast of Maine, Ally uncovers a sinister secret: years ago, a member of the family was the prime suspect in a young woman’s disappearance from the same island. Now, history is repeating itself. Another woman has vanished without a trace. Ally digs into all the dark secrets of the Hawthorne family’s past, but what she discovers may cost her more than her marriage — it may cost her life.