The Shut Mouth Society by James D. Best is the kind of book I like best.
It starts with a rich collector who has discovered an early Abraham Lincoln document. The collector asks two people to authenticate the manuscript: Greg Evarts, a detective, and Patricia Baldwin, a professor. The professor, of course, is not only smart but stinking rich and beautiful. The novel has everything from intrigue and murder to romance.
The story begins in California and progresses to the historical east coast where the reader is introduced to private libraries, secret apartments, and shown how rich and powerful civil war descendants live. Conspiracies and secret societies from the Civil War era are unveiled in such a realistic manner that, when I finished the book, I actually did some research to separate fact from fiction.