The film is adapted from the best-selling novel of the same name by Karen Dionne. It tells the story of the heroine Helena (Daisy Ridley), who on the surface lives an ideal life with her excellent husband and young daughter, but she hides a shocking past: her mother was kidnapped when she was a teenager, and she is the child of the captive and the abuser. Her father, Jacob Holbrook (Ben Mendelsohn), is known as the "King of the Swamp", who imprisoned the mother and daughter in the wilderness for many years. They spent 12 years being controlled by the tyrannical man until he was arrested and sent to prison. After Jacob escaped from prison, killing two prison guards, Helena realized the potential threat her father brought to her family, was forced to face her secret past, and was determined to bring him down.