Brynthwaite Summer by Merry Farmer

Agatha Crimpley is the happiest woman in the cozy, lakeside town of Brynthwaite. She is liked and respected, her father is all set to entrust her with a great deal of responsibility, and she is in love with the dashing and intelligent Mr. Andrew Noble. But Aggie is about to discover that even in the modern and progressive 1880s, who a woman gives her heart to can have shocking consequences.
Andrew Noble might have been born in Africa, but after being raised in England by white parents, he considers himself as much an Englishman as anyone else. But he is not foolish enough to think that falling in love with Aggie will be easy, and when a letter arrives from a former colleague of his adopted father’s, hinting that his origins might not be what he thinks they are, his life takes a major turn.

Can Aggie and Andrew’s love survive the shock of a major turn of fortune? Or will a careless indiscretion prove to Aggie that one’s reputation is only skin deep?