A big thank you to a A Novel Menagerie for Lauren Willig's the Temptation of the Night Jasmine - one of the April giveaways.
From the cover:
After years abroad, Robert, Duke of Dovedale, has returned to England to avenge the murder of his mentor. To uncover the murderer's identity, he must infiltrate the infamous secret Hellfire Club. But the Duke has no idea than even more difficult challenge awaits him - in a mistaken, romantic-minded young lady.
The story starts in present time with an American researcher delving into the archives at Selwick Hall. After finding correspondence to Lady Henrietta Selwick the reader is taken to Christmas Eve, 1803 and Girdings House, Norfolk where we meet Lady Charlotte Landsdowne and her cousin Robert, Duke of Dovedale. Lauren Willig weaves the story around historical facts and throws in romance and intrigue.