Voice out of darkness

She had been dead for thirteen years, ever since she had crashed through the ice on the lonely little pond. Now her foster-sister, Katherine Meredith, was receiving anonymous letters which red, "YOU PUSHED HER!"
To quiet the voice that whispered of a child's brutal murder, Katy returned to the Connecticut town where it had happened. But death was there again. It lingered in the shadows of a steep, dark staircase, rode on the howl of a New England blizzard, and, ugliest of all, deather walked in the form of a friend!