People disappear. Secrets remain... My dearest T., don't believe anything you hear for a moment... 1940: In southwest Ireland, the young and beautiful Lady Charlotte Rathmore is declared dead after mysteriously disappearing by the lake at Blackwater Hall. In London, Nancy Rathmore is mourning Charlotte's death when a letter arrives containing a secret she was sworn to keep - one that will change her life forever. 1958: When she moves into the mysterious Blackwater Hall, Nancy's daughter Hattie soon realizes that nothing above or below the stairs is quite what it seems... and what she discovers is something she can never forget. 2019: Decades later, Ellie Fitzgerald is forced to leave Dublin, heartbroken. Abandoning journalism, she returns to rural Kerry for a new start. But when she discovers a faded letter hidden within the pages of an old book, she finds herself drawn to a long-buried secret. And as Ellie begins to unravel the mystery, it becomes clear that the letter may hold the key to more than just Charlotte's disappearance.