The Rake by Ava Bond

Margot Keating has a dangerous secret about her birth, which no one in polite society can ever find out.
On entering the ton as a vicar’s daughter and spinster, Miss Keating tries her best to keep out of mischief. This is easier said than done, since she is almost immediately thrown into a mystery, surrounding the murder of a prominent duke, some infamous missing diamonds, and–worst of all–Lord Langley, the most tempting rake in London.
Lord Silvester Beresford, Earl of Langley, is famed for his beauty, his charm, his orgies, and for never falling in love.
Thrown together in the most unconventional of ways, can these two opposites work together to uncover the truth about the duke’s death, where the diamonds might be, and whether they actually have more in common than they previously ever thought possible?