Menfreya in the Morning — Victoria Holt

For Harriet Delvaney, the great house of Menfreya, standing like a fortress on the Cornish coast, had always been a citadel of happiness and high spirits. Not until she herself came to Menfreya as a bride did Harriet discover the secret family legend of infidelity, jealousy, and murder. And not until that legend seemed to come dangerously to life did Harriet begin to believe the old story that when the tower clock of Menfreya stopped, it meant that someone was about to die ....