The swimming pool.

In a crumbling mansion, two sisters hide from the world, afraid for their lives The Birches was one of the grand mansions of the 1920s, with a ballroom, tennis courts, and, of course, a swimming pool. But after the crash of ’29, when Lois and Judith’s father killed himself to escape his debts, the family turned the summer home into a fulltime retreat from the world. Decades later, Judith is the queen of New York society, a fast-living beauty whose nerves are beginning to fray, while Lois still lives in the dilapidated old mansion, writing mystery novels to pay the bills. She is about to encounter a mystery of her own. To stave off a nervous breakdown, Judith moves in with her kid sister. Terrified of an unnamed threat, she nails her windows shut and locks the door. Soon, a woman is found dead in the pool—a stranger who bears a shocking resemblance to Judith. In a family with a history of tragedy, a chilling new chapter is about to be written. Judith Chandler has always been the spoiled beauty of the family, but something has gone terribly wrong. With a deadline to meet on her latest detective novel, Lois has no patience to deal with her sister's fears. Until a real-life mystery begins to unfold. For one night, Judith disappears from her locked bedroom, and in the morning, a woman's body is found floating in the swimming pool.