The Hourglass — Elizabeth Gage

They are three children, brought together by loneliness and encroaching tragedy, who forge a friendship that will define their lives. To orphaned Kate, who idolizes Lily and feels a strange kinship to Jordan, this "threeness" becomes the touchstone of her identity.
As adolescents on the eve of separation, they make a promise to meet at their favorite place, an abandoned golf course, in fifteen years. Life sweeps them far from each other and along different paths, and the promise is forgotten.

The Kate, now a successful writer in New York, suddenly remembers the promise. She returns to the town of her youth and makes her way through the darkness to the appointed spot.

What she finds will open the door to a destiny she had never dreamed of for herself. And not until love and obsession have made the sands of time flow in unpredictable directions will the stories of all three friends come to a surprising end.