The Waiting Sands by Susan Howatch
'Dearest Raye,' Decima had written.'I'm writing to ask if you can possibly come up to Ruthven for a few days. My twenty- first birthday falls next Sunday, and it would be such a relief if you could stay until after the celebration dinner party which Charles is giving for me on Saturday night. Please come, Raye. I may be behaving very stupidly by panicking like this, but I would feel so much less frightened if I knew you were beside me at Ruthven till after midnight on Saturday.' Dependable Rachel Lord hasn't heard from her friend Decima for over two years when out of the blue she is invited to Ruthven, the fairy tale Scottish castle that Decima will inherit on her coming of age. Her arrival is met with relief by Decima who is convinced her husband, Charles, means her harm. Is Decima in her right mind? Or is Rachel being duped by her worldlier friend? As the eve of the 21st birthday celebration approaches, a shocking event leaves Rachel in no doubt.