This is the story of two sets of sisters: Jess & Tavy Yates in the present day and Rose & Nell (King Charles II mistress) Gwyn in the 17th century. There's a historical mystery, romance in both timelines, a bit of timeslip, murder in each timeline, and lots of adventure. I've read a couple books by this author and this may be the one I like best so far. She's very descriptive: the historical timeline, especially, really came alive.