Rafael Sabatini 
The Black Swan 

When Priscilla Harradine travels back to England accompanied by the rather dull Major Sands, she has no cause to expect her journey will be anything other than uneventful. But also on board the Centaur is Charles de Bernis — a mysterious and intriguing buccaneer. Just as their friendship is beginning to blossom, a dark figure from de Bernis’ past emerges to propel them into a thrilling and perilous adventure, taking them right to the heart of pirate life.