"The Last Anniversary" is a novel by Liane Moriarty that revolves around the mysterious disappearance of Margot and the impact it has on her family and the residents of Summersate. The story unfolds as the anniversary of her disappearance approaches, prompting the characters to confront their pasts and secrets. The narrative follows Sophie and Thomas, who inherit a house on Summersate Island. As they delve into the island's history and the lives of its inhabitants, they uncover hidden truths and grapple with their own relationships, ultimately leading to revelations about love, loss, and the passage of time.