A Change of Heart — Helen McCloy

Girzel Graeme looked on her father as the embodiment of all that was wise and good. But now her father lay in a hospital hovering between life and death, and the evil that struck him down reached out to claim his daughter.

What terrifying secret did her father's past conceal? What horrifying act could he have committed? And what nameless danger threatened his daughter as she followed the lure of a fabulous jewel into a labyrinth of deceit, on the trail of a mysterious man who could save her faith in her father - or destroy both it and her.