Trevanian 
The Summer of Katya 

In the summer of 1914 Jean-Marc Montjean, a recent graduate from medical school, arrives in the Basque village of Salies in the French Pyrenees to assist the village physician. His first assignment is to treat the brother of a beautiful young woman called Katya Treville. As he comes to know his patient's family, he begins to realise that they are haunted by an old, dark secret — but he can't help falling deeply in love with Katya.
Montjean is warned away from any attempt at romantic involvement by Katya's family, but he is young, hopeful, in love, and certain that his feelings are reciprocated. When he learns that the Trevilles are planning to leave the village forever, he insists on a final meeting with Katya.
During that meeting, the family's secret is revealed, and idyllic romance becomes shattering nightmare. The chilling denouement, reminiscent of Hitchcock at his best, will stay with the reader long after the last page is turned.