This Rough Magic by Mary Stewart

When Lucy Waring's sister Phyllida suggests that she join her for a quiet holiday on the island of Corfu, young English Lucy is overjoyed. Her work as an actress has temporarily come to a halt. She believes there is no finer place to be "at liberty" than the sun-drenched isle of Corfu, the alleged locale for Shakespeare's The Tempest. Even the suspicious actions of the handsome, arrogant son of a famous actor cannot dampen her enthusiasm for this wonderland in the Ionian Sea.

But the peaceful idyll does not last long. A series of incidents, seemingly unconnected - but all surrounded in mystery - throws Lucy's life into a dangerous spin, as fear, danger and death - as well as romance - supplant the former tranquility. Then a human corpse is carried ashore on the incoming tide... And without warning, she found she had stumbled into a nightmare of strange violence, stalked by shadows of terror and sudden death.