The Glass Lake by Maeve Binchy

Night after night the beautiful woman walked beside the serene waters of Lough Glass. Until the day she disappeared, leaving only a boat drifting upside down on the unfathomable lake that gave the town its name. Ravishing Helen McMahon, the Dubliner with film-star looks and unfulfilled dreams, never belonged in Lough Glass, not the way her genial pharmacist-husband Martin belonged, or their spirited daughter Kit. Suddenly, she is gone and Kit is haunted by the memory of her mother, seen through a window, alone at the kitchen table, tears streaming down her face. Now Kit, too, has secrets: of the night she discovered a letter on Martin’s pillow and burned it, unopened. The night her mother was lost. The night everything changed forever…