Vanished — Julie Ellis

Carol Moore had discovered she had a half-brother, Rudy Bartok, who was an artist living in Vienna. Both had eagerly anticipated their first meeting, but Carol had arrived at Rudy's apartment to find he had simply vanished into thin air. Rudy's neighbour, Larry Woods, a journalist and fellow American, volunteered to help Carol solve the mystery. But her bewilderment soon turned to terror when the threats to her life began...