Showing This Rough Magic by Mary Stewart

When Lucy's sister Phyllida suggests that she join her for a quiet holiday on the island of Corfu, Lucy is overjoyed. Her work as an actress has temporarily come to a halt. 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 tranquillity.