The Lake House, a 2015 mystery novel by Australian author Kate Morton, centers on the mysterious disappearance of Theo Edevane, an 11-month-old baby who goes missing from his crib during a party in 1933. The devastated family members each have their own theories about who is responsible, but no one is more affected than his teenage sister, Alice. Seventy years later, Sadie Sparrow, an ambitious young detective, discovers the cold case while visiting her grandfather in Cornwall where the Edevane estate, Loeanneth, is located. With the help of a local policeman, Sadie unravels the mystery. Exploring themes of grief, generational trauma, and family secrets, The Lake House received overwhelming critical praise and landed on best-seller lists in the United States, Australia, and the United Kingdom.

Sadie Sparrow is a detective with the Metropolitan Police Service (the Met) in London. She is investigating the disappearance of a young mother, Maggie Bailey. Because of her past as a pregnant teen who had to give up her daughter (who after all these years is trying to get in touch with her), Sadie finds it hard to accept her colleagues’ belief that Maggie simply abandoned her daughter Caitlyn; there are too many signs that convince her this isn’t what happened. Maggie’s mother, Nancy, also firmly believes that something else happened to her daughter, that she didn’t just leave. Sadie leaks to the press that the Met handled the case poorly. After the newspaper publishes the story, Sadie’s partner Donald knows she was the leak. The superintendent of the Met is livid but doesn’t know who is responsible. Donald tells Sadie he won’t inform on her, but she better take an extended vacation until things settle down.

Sadie goes to visit her grandfather Bertie in the Cornwall countryside. Sadie enjoys running, and on one of her runs she comes across an abandoned lake house. Bertie says that the house, Loeanneth, used to belong to the Edevane family, but they left after the youngest child, Theo, disappeared and was never found. This sparks Sadie’s investigation into the cold case.

Alice, the second-oldest daughter of Anthony and Eleanor Edevane, is a successful detective-story novelist. She is in her eighties now, but she was only 16 when Theo went missing. She has carried a secret these past 70 years, believing she is indirectly responsible for Theo’s disappearance. When Sadie tries to get in touch with Alice to ask her about what happened those many years ago, Alice is forced to revisit the past she has tried to keep buried.

Throughout the novel, the Edevane family history is slowly revealed. Alice’s mother, Eleanor Edevane (née deShiel), falls in love with Anthony Edevane when she is young. They meet when he saves her from being struck by a bus. Anthony is the youngest child of a very wealthy, old, aristocratic family. He is studying to be a surgeon. Eleanor’s mother Constance is not fond of Anthony simply because he doesn’t stand to inherit any of his father’s wealth. Constance and Eleanor have never gotten along. Constance, who has regular affairs with men, is cold, distant, and bitter because her deceased husband made some bad investments and lost nearly all their money, including Eleanor’s favorite childhood home, Loeanneth in Cornwall.

Eleanor and Anthony marry. Soon thereafter all of Anthony’s family dies when the Titanic sinks. He inherits everything. He purchases Loeanneth and even allows Constance to live there with them, though this doesn’t change the old lady at all; she remains cantankerous and embittered.

Eventually, Anthony is drawn to war when hostilities erupt in the summer of 1914. Anthony and Eleanor already have one daughter, Deborah, and Eleanor is pregnant with Alice when Anthony leaves for France (they will have one more daughter together, Clementine). Parting is very difficult.

During the war, Anthony’s longtime best friend Howard, who is like a brother to him, falls in love with a local French girl named Sophie. He wants to desert with her and her young boy. He plans on leaving with them and moving to southern France. Anthony initially tries to stop him, but when he sees how determined Howard is, he helps him by stealing a few supplies from the commissary. They all meet one night in a barn to say farewell. However, while they are getting ready to leave, they hear voices and a barking dog outside. Sophie’s son begins to make noise. Anthony fears for their lives. He tries to smother the boy to make him quiet. Howard throws him back. They are all caught. Howard makes it look as though Anthony was attempting to stop him, saving him. Howard, however, is executed for desertion. Anthony is never the same again and returns home with shell shock symptoms.

Life with Anthony is difficult after the war. He has many episodes where he loses control of himself. He is often depressed and despondent. Eleanor never stops loving him and promises that she will never let anyone know about his problems, something he worries about. One day, Anthony loses control around Eleanor’s dog, Edwina, and beings strangling her. Eleanor stops him, but the girls are there and witness it. Anthony fears he may one day attack one of their children. He has Eleanor promise him she will never let that happen.

Eventually, Eleanor runs into a younger man named Benjamin Munro. The two of them, after several chance encounters, begin a love affair. Eleanor becomes pregnant with Ben’s child, a baby boy, Theo. Ben begins working at the gardens at Loeanneth to be nearer to Eleanor and the baby. Despite Eleanor’s hope that a baby boy would do Anthony well, he actually gets worse. This leads Eleanor to fear for Theo’s safety; she creates an extreme plan to ensure his well-being.

Because Ben is an itinerant worker, Eleanor devises a plan where Ben will take Theo and place him in the care of Ben’s longtime childhood friend, Flo and her husband, making it look like a kidnapping. Late Midsummer’s Eve, Eleanor puts her plan into effect. And it succeeds. No one discovers the truth until years later when Sadie, with the help of Alice and an old police officer who was on the original case, discover what truly happened to Theo. Years after Theo’s disappearance, Eleanor discovered his whereabouts. His name was changed to Bertie. Alice is the first to realize that Sadie’s grandfather Bertie and Theo are one and the same.

The case is solved after many years. Alice and her sister Deborah get closure about the past and celebrate the discovery of their long-lost brother. Sadie and Alice’s assistant, Peter, start dating. Sadie connects with her daughter, and they all live happily ever after.