So Wicked the Heart — Barbara Riefe

A BOLD AND TUMULTUOUS NOVEL OF UNBOUNDED LOVE
Torn from her beautiful home and from the man who had sworn to protect her, Lorna Singleton is kidnapped by a handsome but sadistic pirate. Cast into depravity; she is forced to submit to her abductor. From the sands of the French Riviera to the shores of New England; from the Rock of Gibraltar to the city of Algiers and the intrigue of the Casbah, he carries her across the world. And on that journey her bode will become a fortress of devotion and sacrifice in the struggle against forces of unconscionable evil.