Larsen, Samantha. Lady librarian mystery

"1784 London.Miss Tiffany Woodall didn't murder her half-brother, but she did bury him in the back garden so that she could keep her cottage. Now, the confirmed spinster has to pretend to be Uriah and fulfill his duties as the Duke of Beaufort's librarian while searching Astwell Palace for Uriah's missing diamond pin, the only thing of value they own. Her ruse is almost up when she is discovered by Mr. Samir Lathrop, the local bookseller, who tries to save her from drowning while she's actually just washing up in a lake after burying her brother. Her plan is going by the book, until the rector proposes marriage and she starts to develop feelings for Mr. Lathrop. But when her childhood friend, Tess, comes to visit, Tiffany quickly realizes her secret isn't the only one hidden within these walls. The body of a servant is found, along with a collection of stolen items, and someone else grows mysteriously ill. Can Tiffany solve these mysteries without her own disguise being discovered? If not, she'll lose her cottage and possibly her life."--Amazon