This is a good question in that Emily Cartwright is one of the most important characters in Cambridge. In short, Emily is the narrator. She is thirty years of age and is sent to a West Indian plantation during the three months before she marries Thomas Lockwood.
For Emily, it is the entrance into a "dark, tropical unknown." During this three months on the plantation, Emily struggles with many things. Most significantly, she is quite upset at the rough treatment of the slaves on the plantation. Both Rogers and McDonald try, in vain, to get Emily's attention.
It is only Brown who Emily thinks is of interest. (This is quite ironic because Emily originally reacts to the character out of disgust due to his rape of Christiana and his beating of Cambridge.) Eventually, Emily is convinced that Brown has changed his ways and makes love with Brown during a picnic at Hawthorn Cottage.
Emily witnesses many beatings and even Brown's overthrow of Wilson on the plantation. Emily ends up staying for many more months because she wants to learn more and more. Her plans are to give lectures in England on a tour dealing with this subject and she needs more material. In the meantime, Emily finds out the truth about Mr. Wilson.
The fallout is that Cambridge kills Brown, the one character who Emily is interested in. Emily subsequently has her baby, but the baby dies at birth. Both McDonald and Stella are there to witness this. It is obvious to the reader, then, that Emily's innocence causes her to be overwhelmed by the social institutions present in her country and society at the time.