In a remote Irish castle, the Haloran family is haunted by the mysterious drowning of their youngest daughter, Kathleen, years earlier. As the anniversary of her death approaches, family tensions resurface. Louise, the manipulative wife of John Haloran, plots to secure a share of the family's wealth after her husband suddenly dies from a heart attack. She hides John's body in a lake, crafting a plan to convince Lady Haloran, the family matriarch, that she can communicate with Kathleen's spirit. Louise's scheme takes an unexpected turn when she starts experiencing eerie occurrences around the castle, raising questions about whether Kathleen's death was an accident or something more sinister.

While Louise struggles with her deceptive maneuvers, the remaining Haloran siblings deal with their own secrets and guilt. Richard, the brooding elder brother, is particularly troubled, while the amiable Billy is more concerned with family harmony. A family doctor named Justin Caleb arrives, offering his assistance yet appearing suspiciously intrusive. As supernatural events intensify and an enigmatic ax murderer emerges, long-buried truths begin to surface. The family is thrust into a nightmare where the past collides with the present, and the line between reality and the supernatural blurs, leaving everyone in a state of fear and uncertainty.