The improbably named Ransom Seymour, the Duke of Ainsley, owes a debt to his cousin, the Marquis of Walfort, after a drunken carriage ride two years earlier landed the latter in a wheelchair, while Ainsley escaped with barely a scratch. In the distressing time after her husband's accident, Jeyne, the Marchioness of Walfort, lost the child she carried.
Lady Jayne (yup, the heroine is ACTUALLY called Jeyne Seymour) hates Ainsley and blames him for the accident, her childlessness and the lonely existence of duty and self sacrifice her marriage has become since her husband became paralyzed from the waist down. Now the Marquis has decided that Jeyne would clearly be happier if she had a child, something he can't give her. So he wants Ainsley to father the child instead.
The plan is that Ainsley and Jayne spend a month together, and make love enough times to ensure she gets pregnant. Ainsley is shocked by the proposal, but very attracted to his cousin's wife, so he doesn't protest that much. Jeyne is absolutely appalled, but after a bout of emotional blackmail, pretty much, agrees to the crazy scheme. No points for guessing how long she manages to sustain her hatred for Ainsley after they spend they spend a month together in the countryside.
While the premise for the novel is almost preposterous, and Jeyne does get won over by Ainsley's charm and sexual prowess very quickly, I liked both the protagonists, and was interested in seeing how the plot was going to develop. I also really liked the secondary plot, with Ainsley's mother. I can see why some Amazon reviews question the inclusion of this plot, but if you read the books as a trilogy, you get to know her quite well, and observe her romance with a younger portrait artist. Seeing the culmination of this relationship was very satisfying to me, and since I DID read the whole trilogy, I think the subplot was justified and added to my enjoyment of the third book.