The Hounds of God — Rafael Sabatini

When Don Pedro is shipwrecked off the Cornish coast and captured by the formidable Lady Margaret Trevanion, he expects trouble. What he doesn't expect is to fall in love and run away with Lady Margaret, only to be pursued by his own countrymen. And he certainly hadn't expected that the officers of the Spanish Inquisition would be so ruthless that Don Pedro and Lady Margaret are forced to enlist the help of the Queen of England herself.