In 1935, six-year-old Emily Evans vanishes from her family's vacation home on a remote Minnesota lake. Her father commits suicide, and her mother and two older sisters spend the rest of their lives at the lake house, keeping a decades-long vigil. Sixty years later, Lucy, the middle sister, lives in the lake house alone. Before her death, she writes the story of that summer in a notebook that she leaves, along with the house, to her grandniece, Justine. For Justine, the lake house offers an escape from her manipulative boyfriend and gives her daughters the home she never had. But the lake is isolated and eerie. Her only neighbour is a strange old man who seems to know more about the summer of 1935 than he's telling. Soon Justine's troubled oldest daughter becomes obsessed with Emily's disappearance, her mother arrives to steal her inheritance, and the man she left launches a dangerous plan to get her back.