Lord Corsair by Sydney Jane Baily

A treacherous world of pistols, plunder, and passion
Miss Beryl Angsley, relishing a final few months of freedom before marriage, accompanies her father across the globe on a mission of diplomacy only to find herself kidnapped by Chinese pirates in the South China Sea.
British privateer, Philip Carruthers, on a secret undertaking for Queen Victoria, has at last found the treasure he’s sought for two years. Unfortunately, he also finds a captive Englishwoman.
Duty-bound to rescue her, he risks his ship, his crew, and his cat to return Lady Angsley to her father. In the midst of a dangerous world of pistols and plunder, Captain Carruthers goes from privateer to pirate in order to steal the heart of a lady.
A secret royal mission or the life of a lady? Which will he choose?