Clarissa, the heroine, is the daughter of a courtesan, and breathtakingly beautiful (think Elizabeth Taylor in her teens). Her mother gives her to the hero in lieu of payment of an old debt she owes him (no, he was never her customer). Trouble is, Clarissa was raised in an extremely strict girls' school and is not only a complete innocent, but has extremely strict morals as well, and she has no intention of fulfilling the deal her mother made with the hero. She simply wants to escape from her mother's clutches and find work as a governess or teacher. The hero figures out pretty quickly that she is an innocent, but still wants his payment. On the other hand, he is a somewhat honourable man and won't force her into anything she doesn't want to do, so he temporizes by telling her she can be his guest while he looks for a job for her, all the while attempting to seduce her but falling more and more desperately in love with her.
Lovely story, although I'm not sure how things will fare for the couple after the book ends - the courtesan mother is still around and judging from the description of her character at the beginning of the book, she will milk them for everything she can get.