Julie Garwood's historical romances are some of my favorite books.
This one almost qualifies as a mystery as well as a romance. This one is even more adventurous than Lion's Lady. Of course how could it not be...it starts out with someone trying to kill her. The dark moments are not too dark in this one. It is a lighter book than Ransom and way lighter than all her contemporary novels (They are a bit too dark for my taste.)
To set up the connection with the others - Caine's friend Lyon (character in this book) is the male lead in Lion's Lady. Jade (female lead) is the sister of Nathan the lead male in The Gift. I cannot tie in the 4th Castles without spoiling plot lines in the others. You can read these in any order, but the surprises and plots are more fun in order:
Lion's Lady, Guardian Angel, The Gift, Castles.