The rising tide - Molly Keane

In 1900 Lady Charlotte French-McGrath is mistress of Garonlea, a huge gothic house in Ireland.
She rules her household and her family -- husband Ambrose and children Muriel, Enid, Violet, Diana and Desmond -- with a rod of iron.
Desmond's marriage to the beautiful, lively Cynthia and, several years later, the onset of the First World War are the two events which finally, and irrevocably, break Lady Charlotte's matriarchal hold.
Cynthia enters the Jazz Age and on the surface her life passes in a whirl of fox-hunting, drinking and love-making.

But the ghosts of Garonlea are only biding their time: they know the source of their power, a secret handed on from one generation to the next...