Heigl stars as Tessa Connover, who is barely coping with the end of her marriage when her ex-husband, David (Stults), becomes happily engaged to Julia Banks (Dawson)-not only bringing Julia into the home they once shared but also into the life of their daughter, Lilly (Isabella Rice).

Trying to settle into her new role as a wife and a stepmother, Julia believes she has finally met the man of her dreams, the man who can help her put her own troubled past behind her. But Tessa's jealousy soon takes a pathological turn until she will stop at nothing to turn Julia's dream into her ultimate nightmare.