As usual, if you're going to write about a subject in historical fiction, you need to research the background to make it authentic. I hate making things up, so I dive into the Internet or purchase books, as I did for my first volume. When I was in grade school, I hated history. Now that I am a writer, I enjoy taking the deep dive into period times.
How he gets there and who sent him, I'll leave for you to read. However, I also tied into the story the sad fact that slave trading was a practice by the British in the 1700's. Great Britain abolished the slave trade in 1808, and all existing slaves were emancipated in 1834. Prior to that time, however, the treatment of slaves on sugar plantations was appalling to say the least. There is no romance in the ill treatment of humans by fellow beings.