The Borgia Mistress by Sara Poole (historical fiction)

I've read The Borgia Betrayal, the second book in this series, but not Poison, the first.  I enjoyed this one more than The Betrayal, even though it suffers a little bit from reminding the reader of stuff that's already happened.  The twist was truly shocking, and I didn't figure it out before the protagonist did.  The ending is tad corny, but not as corny as most of The Betrayal.  The descriptions of the Vatican and the characterization of Rodrigo Borgia, Pope Alexander VI, are very good across both books.