From the jacket

When Glen Chandler first removed the combs from Dina's pale hair and said, "You're my winter girl," Dina seemed to surrender her will to him forever. She married Glen without even seeing High Towers, the remote Victorian estate whose windows, like eyes, still watched the lake where Glen's mother had once drowned. A summer person herself, Dina did not know that the Chandlers were winter people-as cold is the ice around High Towers. She did not know they could turn her very heart to ice.

Dina had often heard of Glen's father, the world-renowned portrait painter. Glen himself had once shown great promise as a sculptor, and he seemed obsessed with the alabaster head he was doing of her. Yet before their marriage, Glen had kept the all-important fact from Dina: he had a twin sister. It is soon clear that it is to Glynis, his twin as dark as Dina is fair, that Glen listens. Always inseparable, always united, they seem to stand as one against Dina-as if playing some wild game of their own.

Dina soon finds herself in mortal terror. Yet what Glynis' evil influence can do to Glen and to her marriage is only the beginning of the high danger Dina will face. For this novel might be said to be about demon possession. And all those at High Towers are haunted, possessed.