IMPOSTOR by Elaine Fox
Flynn Patrick is leading a typical 20th-century life when he attends the wedding of an old friend at a country estate in England. Though he arrives stressed out, with girlfriend troubles and parental issues, he is soon distracted by an uneasy sense of having been to the house before. Long before. What he doesn't realize is that he'll be returning to that long-ago time on this very day.
Melisande St. Claire is escaping a disastrous betrothal to a cruel and corrupt earl when she meets Flynn Patrick. Though he looks startlingly like the prince in her recurring dreams, he is clearly crazy. Handsome, but crazy. Still, she's stuck with him for now, as he's the only one who can help her get to London, and the aunt who can save her from her betrothal.
Though they start out as opposites, passion quickly flares between them. As Melisande begins to realize her reputation will be in tatters long before she reaches London, she wrestles with whether to allow her virtue to be ruined along with it.
Flynn, however, is all too conscious of the fact that he has to return to his own home, his own time, and he doesn't want to leave a devastated Melisande behind. But in securing her future by pretending to be the long-lost son of a duke, he drastically alters his own. And while Melisande is not sure if Flynn is telling the truth or not, she's falling so hard for him she almost doesn't care that he's an impostor.