Black Amber — Phyllis A. Whitney

To Tracy Hubbard, at home in New York, a masquerade had seemed the only possible way to track down the answer to a tragedy for which she felt partly responsible. But now that she was in Istanbul, an impostor in the exotic household of Sylvana Erim, Tracy was baffled and alarmed by a series of mystifying events and drawn, in spite of herself, into a whirlpool of conspiracy and intrigue.
In the abandoned ruins of a palace she overhears a heated argument in Turkish-the only word she can understand is her own name. She watches a small, unlighted boat pay a nocturnal visit to the dock of the villa's garden. Unknown hands mark a disturbing passage in a book with a string of black amber beads.
She has come here as an assistant to Miles Radburn, the well-known artist. Radburn appears to hold the answers to several life or death questions. Is he suffering grief over the death of his young wife, or is he responsible for some loathsome secret that lies hidden in the past? Tracy finds it requires all her own stubborn defiance to resist this violent man who can at times be so strangely tender. There is no one she can trust in the hostile and enigmatic household. Suddenly Tracy realizes that she knows too much and that her very life is in danger.