"Man of My Dreams" by Johanna Lindsey - 405 pages
Megan is the most desirable beauty in the area and she has set her sights on Ambrose St. James, Duke of Wrothston. He needs to hide, so he poses as Devlin Jefferys, a horse trainer who is helping her father set up a breeding stable. She doesn't want to fall for a horse trainer and he doesn't want to fall for anyone. Yet once they meet, neither can think of being with anyone else.