Sleeping Murder; Miss Marple's Last Case by Agartha

Soon after Gwenda moves into her new home, odd things start to happen. Despite her best efforts to modernize the house, she only succeeds in dredging up its past. Worse, she feels an irrational sense of terror every time she climbs the stairs. Terrified, Gwenda turns to Jane Marple to exorcise her ghosts. Between them, they try to solve a 'perfect' crime committed many years before ..